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Configuring and managing virtualization

Red Hat Enterprise Linux 8

Setting up your host, creating and administering virtual machines, and understanding virtualization features in Red Hat Enterprise Linux 8

Red Hat Customer Content Services

Abstract

This document describes how to manage virtualization in Red Hat Enterprise Linux 8 (RHEL 8). In addition to general information about virtualization, it describes how to manage virtualization using command-line utilities, as well as using the web console.

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Chapter 1. Virtualization in RHEL 8 - an overview

If you are unfamiliar with the concept of virtualization or its implementation in Linux, the following sections provide a general overview of virtualization in RHEL 8: its basics, advantages, components, and other possible virtualization solutions provided by Red Hat.

1.1. What is virtualization?

RHEL 8 provides the virtualization functionality, which enables a machine running RHEL 8 to host multiple virtual machines (VMs), also referred to as guests. VMs use the host’s physical hardware and computing resources to run a separate, virtualized operating system (guest OS) as a user-space process on the host’s operating system.

In other words, virtualization makes it possible to have operating systems within operating systems.

VMs enable you to safely test software configurations and features, run legacy software, or optimize the workload efficiency of your hardware. For more information on the benefits, see Section 1.2, “Advantages of virtualization”.

For more information on what virtualization is, see the Red Hat Customer Portal.

To try out virtualization in RHEL 8, see Chapter 2, Getting started with virtualization.

Note

In addition to RHEL 8 virtualization, Red Hat offers a number of specialized virtualization solutions, each with a different user focus and features. For more information, see Section 1.5, “Red Hat virtualization solutions”.

1.2. Advantages of virtualization

Using virtual machines (VMs) has the following benefits in comparison to using physical machines:

  • Flexible and fine-grained allocation of resources

    A VM runs on a host machine, which is usually physical, and physical hardware can also be assigned for the guest OS to use. However, the allocation of physical resources to the VM is done on the software level, and is therefore very flexible. A VM uses a configurable fraction of the host memory, CPUs, or storage space, and that configuration can specify very fine-grained resource requests.

    For example, what the guest OS sees as its disk can be represented as a file on the host file system, and the size of that disk is less constrained than the available sizes for physical disks.

  • Software-controlled configurations

    The entire configuration of a VM is saved as data on the host, and is under software control. Therefore, a VM can easily be created, removed, cloned, migrated, operated remotely, or connected to remote storage.

  • Separation from the host

    A guest OS runs on a virtualized kernel, separate from the host OS. This means that any OS can be installed on a VM, and even if the guest OS becomes unstable or is compromised, the host is not affected in any way.

  • Space and cost efficiency

    A single physical machine can host a large number of VMs. Therefore, it avoids the need for multiple physical machines to do the same tasks, and thus lowers the space, power, and maintenance requirements associated with physical hardware.

  • Software compatibility

    Because a VM can use a different OS than its host, virtualization makes it possible to run applications that were not originally released for your host OS. For example, using a RHEL 6 guest OS, you can run applications released for RHEL 6 on a RHEL 8 host system.

    Note

    Not all operating systems are supported as a guest OS in a RHEL 8 host. For details, see Section 20.2, “Recommended features in RHEL 8 virtualization”.

1.3. Virtual machine components and their interaction

Virtualization in RHEL 8 consists of the following principal software components:

Hypervisor

The basis of creating virtual machines (VMs) in RHEL 8 is the hypervisor, a software layer that controls hardware and enables running multiple operating systems on a host machine.

The hypervisor includes the Kernel-based Virtual Machine (KVM) module and virtualization kernel drivers, such as virtio and vfio. These components ensure that the Linux kernel on the host machine provides resources for virtualization to user-space software.

At the user-space level, the QEMU emulator simulates a complete virtualized hardware platform that the guest operating system can run in, and manages how resources are allocated on the host and presented to the guest.

In addition, the libvirt software suite serves as a management and communication layer, making QEMU easier to interact with, enforcing security rules, and providing a number of additional tools for configuring and running VMs.

XML configuration

A host-based XML configuration file (also known as a domain XML file) determines all settings and devices in a specific VM. The configuration includes:

  • Metadata such as the name of the VM, time zone, and other information about the VM.
  • A description of the devices in the VM, including virtual CPUs (vCPUS), storage devices, input/output devices, network interface cards, and other hardware, real and virtual.
  • VM settings such as the maximum amount of memory it can use, restart settings, and other settings about the behavior of the VM.

For more information on the contents of an XML configuration, see sample VM XML configuration.

Component interaction

When a VM is started, the hypervisor uses the XML configuration to create an instance of the VM as a user-space process on the host. The hypervisor also makes the VM process accessible to the host-based interfaces, such as the virsh, virt-install, and guestfish utilities, or the web console GUI.

When these virtualization tools are used, libvirt translates their input into instructions for QEMU. QEMU communicates the instructions to KVM, which ensures that the kernel appropriately assigns the resources necessary to carry out the instructions. As a result, QEMU can execute the corresponding user-space changes, such as creating or modifying a VM, or performing an action in the VM’s guest operating system.

Note

While QEMU is an essential component of the architecture, it is not intended to be used directly on RHEL 8 systems, due to security concerns. Therefore, using qemu-* commands is not supported by Red Hat, and it is highly recommended to interact with QEMU using libvirt.

For more information on the host-based interfaces, see Section 1.4, “Tools and interfaces for virtualization management”.

Figure 1.1. RHEL 8 virtualization architecture

virt architecture

1.4. Tools and interfaces for virtualization management

You can manage virtualization in RHEL 8 using the command-line interface (CLI) or several graphical user interfaces (GUIs).

Command-line interface

The CLI is the most powerful method of managing virtualization in RHEL 8. Prominent CLI commands for virtual machine (VM) management include:

  • virsh - A versatile virtualization command-line utility and shell with a great variety of purposes, depending on the provided arguments. For example:

    • Starting and shutting down a VM - virsh start and virsh shutdown
    • Listing available VMs - virsh list
    • Creating a VM from a configuration file - virsh create
    • Entering a virtualization shell - virsh

    For more information, see the virsh(1) man page.

  • virt-install - A CLI utility for creating new VMs. For more information, see the virt-install(1) man page.
  • virt-xml - A utility for editing the configuration of a VM.
  • guestfish - A utility for examining and modifying VM disk images. For more information, see the guestfish(1) man page.

Graphical interfaces

You can use the following GUIs to manage virtualization in RHEL 8:

  • The RHEL 8 web console, also known as Cockpit, provides a remotely accessible and easy to use graphical user interface for managing VMs and virtualization hosts.

    For instructions on basic virtualization management with the web console, see Chapter 5, Managing virtual machines in the web console.

  • The Virtual Machine Manager (virt-manager) application provides a specialized GUI for managing VMs and virtualization hosts.

    Important

    Although still supported in RHEL 8, virt-manager has been deprecated. The web console is intended to become its replacement in a subsequent release. It is, therefore, recommended that you get familiar with the web console for managing virtualization in a GUI.

    However, in RHEL 8, some features may only be accessible from either virt-manager or the command line. For details, see Section 5.4, “Differences between virtualization features in Virtual Machine Manager and the web console”.

  • The Gnome Boxes application is a lightweight graphical interface to view and access VMs and remote systems. Gnome Boxes is primarily designed for use on desktop systems.

    Important

    Gnome Boxes is provided as a part of the GNOME desktop environment and is supported on RHEL 8, but Red Hat recommends that you use the web console for managing virtualization in a GUI.

Additional resources

1.5. Red Hat virtualization solutions

The following Red Hat products are built on top of RHEL 8 virtualization features and expand the KVM virtualization capabilities available in RHEL 8. In addition, many limitations of RHEL 8 virtualization do not apply to these products:

Red Hat Virtualization (RHV)

RHV is designed for enterprise-class scalability and performance, and enables the management of your entire virtual infrastructure, including hosts, virtual machines, networks, storage, and users from a centralized graphical interface.

Red Hat Virtualization can be used by enterprises running large deployments or mission-critical applications. Examples of large deployments suited to Red Hat Virtualization include databases, trading platforms, and messaging systems that must run continuously without any downtime.

For more information about Red Hat Virtualization, see the Red Hat Customer Portal or the Red Hat Virtualization documentation suite.

To download a fully supported 60-day evaluation version of Red Hat Virtualization, see the Red Hat Customer Portal.

Red Hat OpenStack Platform (RHOSP)

Red Hat OpenStack Platform offers an integrated foundation to create, deploy, and scale a secure and reliable public or private OpenStack cloud.

For more information about Red Hat OpenStack Platform, see the Red Hat Customer Portal or the Red Hat OpenStack Platform documentation suite.

Note

For details on virtualization features not supported on RHEL but supported on RHV or RHOSP, see Section 20.3, “Unsupported features in RHEL 8 virtualization”.

In addition, specific Red Hat products provide operating-system-level virtualization, also known as containerization:

  • Containers are isolated instances of the host OS and operate on top of an existing OS kernel. For more information on containers, see the Red Hat Customer Portal.
  • Containers do not have the versatility of KVM virtualization, but are more lightweight and flexible to handle. For a more detailed comparison, see the Introduction to Linux Containers.

Chapter 2. Getting started with virtualization

To start using virtualization in RHEL 8, follow the steps below. The default method for this is using the command-line interface (CLI), but for user convenience, some of the steps can be completed in the the web console GUI.

  1. Enable the virtualization module and install the virtualization packages - see Section 2.1, “Enabling virtualization”.

  2. Create a virtual machine (VM):

  3. Start the VM:

  4. Connect to the VM:

Note

The web console currently provides only a subset of VM management functions, so using the command line is recommended for advanced use of virtualization in RHEL 8.

2.1. Enabling virtualization

To use virtualization in RHEL 8, you must enable the virtualization module, install virtualization packages, and ensure your system is configured to host virtual machines (VMs).

Prerequisites

  • Red Hat Enterprise Linux 8 is installed and registered on your host machine.

  • Your system meets the following hardware requirements to work as a virtualization host:

    • The architecture of your host machine supports KVM virtualization.

    • The following minimum system resources are available:

      • 6 GB free disk space for the host, plus another 6 GB for each intended VM.
      • 2 GB of RAM for the host, plus another 2 GB for each intended VM.

Procedure

  1. Install the packages in the RHEL 8 virtualization module: 

    # yum module install virt

  2. Install the virt-install and virt-viewer packages: 

    # yum install virt-install virt-viewer

  3. Start the libvirtd service. 

    # systemctl start libvirtd

  4. Verify that your system is prepared to be a virtualization host: 

    # virt-host-validate
[...]
QEMU: Checking for device assignment IOMMU support         : PASS
QEMU: Checking if IOMMU is enabled by kernel               : WARN (IOMMU appears to be disabled in kernel. Add intel_iommu=on to kernel cmdline arguments)
LXC: Checking for Linux >= 2.6.26                          : PASS
[...]
LXC: Checking for cgroup 'blkio' controller mount-point    : PASS
LXC: Checking if device /sys/fs/fuse/connections exists    : FAIL (Load the 'fuse' module to enable /proc/ overrides)

  5. If all virt-host-validate checks return a PASS value, your system is prepared for creating VMs.

    If any of the checks return a FAIL value, follow the displayed instructions to fix the problem.

    If any of the checks return a WARN value, consider following the displayed instructions to improve virtualization capabilities.

Additional information

  • Note that if virtualization is not supported by your host CPU, virt-host-validate generates the following output: 

    QEMU: Checking for hardware virtualization: FAIL (Only emulated CPUs are available, performance will be significantly limited)

    However, attempting to create VMs on such a host system will fail, rather than have performance problems.

2.2. Creating virtual machines

To create a virtual machine (VM) in RHEL 8, use the command line interface or the RHEL 8 web console.

Prerequisites

  • Virtualization is installed and enabled on your system.

  • You have sufficient amount of system resources to allocate to your VMs, such as disk space, RAM, or CPUs. The recommended values may vary significantly depending on the intended tasks and workload of the VMs.

    Warning

    Installing from a host CD-ROM or DVD-ROM device is not possible in RHEL 8. If you select a CD-ROM or DVD-ROM as the installation source when using any VM installation method available in RHEL 8, the installation will fail. For more information, see the Red Hat Knowledgebase.

2.2.1. Creating virtual machines using the command-line interface

To create a virtual machine (VM) on your RHEL 8 host using the virt-install utility, follow the instructions below.

Prerequisites

  • Virtualization is enabled on your host system.

  • An operating system (OS) installation source is available locally or on a network. This can be one of the following:

    • An ISO image of an installation medium
    • A disk image of an existing VM installation
  • Optional: A Kickstart file can be provided for faster and easier configuration of the installation.

Procedure

To create a VM and start its OS installation, use the virt-install command, along with the following mandatory arguments:

  • The name of the new machine
  • The amount of allocated memory
  • The number of allocated virtual CPUs (vCPUs)
  • The type and size of the allocated storage
  • The type and location of the OS installation source

Based on the chosen installation method, the necessary options and values can vary. See below for examples:

  • The following creates a VM named demo-guest1 that installs the Windows 10 OS from an ISO image locally stored in the /home/username/Downloads/Win10install.iso file. This VM is also allocated with 2048 MiB of RAM and 2 vCPUs, and an 80 GiB qcow2 virtual disk is automatically configured for the VM. 

    # virt-install --name demo-guest1 --memory 2048 --vcpus 2 --disk size=80 --os-variant win10 --cdrom /home/username/Downloads/Win10install.iso

  • The following creates a VM named demo-guest2 that uses the /home/username/Downloads/rhel8.iso image to run a RHEL 8 OS from a live CD. No disk space is assigned to this VM, so changes made during the session will not be preserved. In addition, the VM is allocated with 4096 MiB of RAM and 4 vCPUs. 

    # virt-install --name demo-guest2 --memory 4096 --vcpus 4 --disk none --livecd --os-variant rhel8.0 --cdrom /home/username/Downloads/rhel8.iso

  • The following creates a RHEL 8 VM named demo-guest3 that connects to an existing disk image, /home/username/backup/disk.qcow2. This is similar to physically moving a hard drive between machines, so the OS and data available to demo-guest3 are determined by how the image was handled previously. In addition, this VM is allocated with 2048 MiB of RAM and 2 vCPUs. 

    # virt-install --name demo-guest3 --memory 2048 --vcpus 2 --os-variant rhel8.0 --import --disk /home/username/backup/disk.qcow2

    Note that the --os-variant option is highly recommended when importing a disk image. If it is not provided, the performance of the created VM will be negatively affected.

  • The following creates a VM named demo-guest4 that installs from the http://example.com/OS-install URL. For the installation to start successfully, the URL must contain a working OS installation tree. In addition, the OS is automatically configured using the /home/username/ks.cfg kickstart file. This VM is also allocated with 2048 MiB of RAM, 2 vCPUs, and a 160 GiB qcow2 virtual disk. 

    # virt-install --name demo-guest4 --memory 2048 --vcpus 2 --disk size=160 --os-variant rhel8.0 --location http://example.com/OS-install --initrd-inject /home/username/ks.cfg --extra-args="ks=file:/ks.cfg console=tty0 console=ttyS0,115200n8"

  • The following creates a VM named demo-guest5 that installs from a RHEL8.iso image file in text-only mode, without graphics. It connects the guest console to the serial console. The VM has 16384 MiB of memory, 16 vCPUs, and 280 GiB disk. This kind of installation is useful when connecting to a host over a slow network link. 

    # virt-install --name demo-guest5 --memory 16384 --vcpus 16 --disk size=280 --os-variant rhel8.0 --location RHEL8.iso --graphics none --extra-args='console=ttyS0'

  • The following creates a VM named demo-guest6, which has the same configuration as demo-guest5, but resides on the 10.0.0.1 remote host. 

    # virt-install --connect qemu+ssh://root@10.0.0.1/system --name demo-guest6 --memory 16384 --vcpus 16 --disk size=280 --os-variant rhel8.0 --location RHEL8.iso --graphics none --extra-args='console=ttyS0'

If the VM is created successfully, a virt-viewer window opens with a graphical console of the VM and starts the guest OS installation.

Troubleshooting

  • If virt-install fails with a cannot find default network error:

    1. Ensure that the libvirt-daemon-config-network package is installed: 

      # yum info libvirt-daemon-config-network
Installed Packages
Name         : libvirt-daemon-config-network
[...]

    2. Verify that the libvirt default network is active and configured to start automatically: 

      # virsh net-list --all
 Name      State    Autostart   Persistent
--------------------------------------------
 default   active   yes         yes

    3. If it is not, activate the default network and set it to auto-start: 

      # virsh net-autostart default
Network default marked as autostarted

# virsh net-start default
Network default started

      1. If activating the default network fails with the following error, the libvirt-daemon-config-network package has not been installed correctly. 

        error: failed to get network 'default'
error: Network not found: no network with matching name 'default'

        To fix this, re-install libvirt-daemon-config-network. 

        # yum reinstall libvirt-daemon-config-network

      2. If activating the default network fails with an error similar to the following, a conflict has occurred between the default network’s subnet and an existing interface on the host. 

        error: Failed to start network default
error: internal error: Network is already in use by interface ens2

        To fix this, use the virsh net-edit default command and change the 192.168.122.* values in the configuration to a subnet not already in use on the host.

Additional resources

  • A number of other options can be specified for virt-install to further configure the VM and its OS installation. For details, see the virt-install man page.
  • If you already have a functional VM, you can clone it to quickly create a new VM with the same configuration and data. For details, see Chapter 8, Cloning virtual machines.

2.2.2. Creating virtual machines and installing guest operating systems using the web console

To manage virtual machines (VMs) in a GUI on a RHEL 8 host, use the web console. The following sections provide information on how to use the RHEL 8 web console to create VMs and install guest operating systems on them.

2.2.2.1. Creating virtual machines using the web console

To create a virtual machine (VM) on the host machine to which the web console is connected, follow the instructions below.

Prerequisites

  • To use the web console to manage VMs, install the web console VM plug-in.
  • You have sufficient amount of system resources to allocate to your VMs, such as disk space, RAM, or CPUs. The recommended values may vary significantly depending on the intended tasks and workload of the VMs.

Procedure

  1. In the Virtual Machines interface of the web console, click Create VM.

    The Create New Virtual Machine dialog appears.

    cockpit create new vm

  2. Enter the basic configuration of the VM you want to create.

    • Name - The name of the VM.
    • Installation Type - The installation can use a local installation medium, a URL, a PXE network boot, or download an OS from a limited set of operating systems.
    • Operating System - The VM’s operating system. Note that Red Hat provides support only for a limited set of guest operating systems.
    • Storage - The type of storage with which to configure the VM.
    • Size - The amount of storage space with which to configure the VM.
    • Memory - The amount of memory with which to configure the VM.
    • Run unattended installation - Whether or not to run the installation unattended.
    • Immediately Start VM - Whether or not the VM will start immediately after it is created.

  3. Click Create.

    The VM is created. If the Immediately Start VM checkbox is selected, the VM will immediately start and begin installing the guest operating system.

Additional resources

2.2.2.2. Creating virtual machines by importing disk images using the web console

To create a virtual machine (VM) by importing a disk image of an existing VM installation, follow the instructions below.

Prerequisites

  • To use the web console to manage VMs, install the web console VM plug-in.
  • You have sufficient amount of system resources to allocate to your VMs, such as disk space, RAM, or CPUs. The recommended values can vary significantly depending on the intended tasks and workload of the VMs.
  • Make sure you have a disk image of an existing VM installation

Procedure

  1. In the Virtual Machines interface of the web console, click Import VM.

    The Import A Virtual Machine dialog appears.

    cockpit import vm

  2. Enter the basic configuration of the VM you want to create.

    • Name - The name of the VM.
    • Connection - The type of libvirt connection, system or session.
    • Installation Source - The existing disk image of a VM on the host system.
    • Operating System - The VM’s operating system. Note that Red Hat provides support only for a limited set of guest operating systems.
    • Memory - The amount of memory with which to configure the VM.
    • Immediately Start VM - Whether or not the VM will start immediately after it is created.
  3. Click Import.

2.2.2.3. Installing guest operating systems using the web console

The first time a virtual machine (VM) loads, you must install an operating system on the VM.

Note

If the Immediately Start VM checkbox in the Create New Virtual Machine dialog is checked, the installation routine of the operating system starts automatically when the VM is created.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM on which you want to install a guest OS.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for installing and deleting the VM.

    cockpit UEFI overview

  2. Optional: Change the firmware.

    Note

    You can change the firmware only if you had not selected the Immediately Start VM check box in the Create New Virtual Machine dialog, and the OS has not already been installed on the VM.

    1. Click the highlighted firmware.

      cockpit vm overview

    2. In the Change Firmware window, select the desired firmware.

      cockpit vm firmware
    3. Click Save.

  3. Click Install.

    The installation routine of the operating system runs in the VM console.

Troubleshooting

  • If the installation routine fails, the VM must be deleted and recreated.

2.3. Starting virtual machines

To start a virtual machine (VM) in RHEL 8, you can use the command line interface or the web console GUI.

Prerequisites

2.3.1. Starting a virtual machine using the command-line interface

You can use the command line interface to start a shutdown virtual machine (VM) or restore a saved VM. Follow the procedure below.

Prerequisites

  • An inactive VM that is already defined.
  • The name of the VM.

  • For remote VMs:

    • The IP address of the host where the VM is located.
    • Root access privileges to the host.

Procedure

  • For a local VM, use the virsh start utility.

    For example, the following command starts the demo-guest1 VM. 

    # virsh start demo-guest1
Domain demo-guest1 started

  • For a VM located on a remote host, use the virsh start utility along with the QEMU+SSH connection to the host.

    For example, the following command starts the demo-guest1 VM on the 192.168.123.123 host. 

    # virsh -c qemu+ssh://root@192.168.123.123/system start demo-guest1

root@192.168.123.123's password:
Last login: Mon Feb 18 07:28:55 2019

Domain demo-guest1 started

Additional Resources

  • For more virsh start arguments, use virsh start --help.
  • For simplifying VM management on remote hosts, see modifying your libvirt and SSH configuration.
  • You can use the virsh autostart utility to configure a VM to start automatically when the host boots up. For more information about autostart, see the virsh autostart help page.

2.3.2. Starting virtual machines using the web console

If a virtual machine (VM) is in the shut off state, you can start it using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM you want to start.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Run.

    The VM starts, and you can connect to its console or graphical output.

  3. Optional: To set up the VM to start automatically when the host starts, click the Autostart checkbox.

Additional resources

2.4. Connecting to virtual machines

To interact with a virtual machine (VM) in RHEL 8, you need to connect to it by doing one of the following:

If the VMs to which you are connecting are on a remote host rather than a local one, you can optionally configure your system for more convenient access to remote hosts.

Prerequisites

2.4.1. Interacting with virtual machines using the web console

To interact with a virtual machine (VM) in the RHEL 8 web console, you need to connect to the VM’s console. These include both graphical and serial consoles.

2.4.1.1. Viewing the virtual machine graphical console in the web console

Using the virtual machine (VM) console interface, you can view the graphical output of a selected VM in the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose graphical console you want to view.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Consoles.

    The graphical console appears in the web interface.

cockpit graphical console in cockpit

You can interact with the VM console using the mouse and keyboard in the same manner you interact with a real machine. The display in the VM console reflects the activities being performed on the VM.

Note

The host on which the web console is running may intercept specific key combinations, such as Ctrl+Alt+Del, preventing them from being sent to the VM.

To send such key combinations, click the Send key menu and select the key sequence to send.

For example, to send the Ctrl+Alt+Del combination to the VM, click the Send key menu and select the Ctrl+Alt+Del menu entry.

Additional resources

2.4.1.2. Viewing the graphical console in a remote viewer using the web console

You can view the graphical console of a selected virtual machine (VM) in a remote viewer, such as virt-viewer. For instructions, see below.

Note

You can launch Virt Viewer from within the web console. Other VNC and SPICE remote viewers can be launched manually.

Prerequisites

  • To use the web console to manage VMs, install the web console VM plug-in.
  • Ensure that both the host and the VM support a graphical interface.

  • Before you can view the graphical console in Virt Viewer, Virt Viewer must be installed on the machine to which the web console is connected.

    To view information on installing Virt Viewer, select the Graphics Console in Desktop Viewer Console Type and click More Information in the Consoles window.

    cockpit install vv info
Note

Some browser extensions and plug-ins do not allow the web console to open Virt Viewer.

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose graphical console you want to view.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Consoles.

    The graphical console appears in the web interface.

  3. Select the Graphics Console in Desktop Viewer Console Type.

    cockpit launch graphical console in vv

  4. Click Launch Remote Viewer.

    The graphical console appears in Virt Viewer.

    virt viewer GUI

You can interact with the VM console using the mouse and keyboard in the same manner you interact with a real machine. The display in the VM console reflects the activities being performed on the VM.

Note

The server on which the web console is running can intercept specific key combinations, such as Ctrl+Alt+Del, preventing them from being sent to the VM.

To send such key combinations, click the Send key menu and select the key sequence to send.

For example, to send the Ctrl+Alt+Del combination to the VM, click the Send key menu and select the Ctrl+Alt+Del menu entry.

Troubleshooting

  • If launching a remote viewer graphics console in the web console does not work or is not optimal, you can use the Manual Connection information, displayed on the right side of the Graphics Console pane.

    cockpit manual viewer info

    Enter the information in a SPICE or VNC viewer application, such as Virt Viewer.

Additional resources

2.4.1.3. Viewing the virtual machine serial console in the web console

You can view the serial console of a selected virtual machine (VM) in the RHEL 8 web console. This is useful when the host machine or the VM is not configured with a graphical interface.

Prerequisites

Procedure

  1. In the Virtual Machines pane, click the row of the VM whose serial console you want to view.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Consoles.

    The graphical console appears in the web interface.

  3. Select the Serial Console Console Type.

    The serial console appears in the web interface.

    cockpit serial console in cockpit

You can disconnect and reconnect the serial console from the VM.

  • To disconnect the serial console from the VM, click Disconnect.
  • To reconnect the serial console to the VM, click Reconnect.

Additional resources

2.4.2. Opening a virtual machine graphical console using Virt Viewer

To connect to a graphical console of a KVM virtual machine (VM) and open it in the Virt Viewer desktop application, follow the procedure below.

Prerequisites

  • Your system, as well as the VM you are connecting to, must support graphical displays.
  • If the target VM is located on a remote host, connection and root access privileges to the host are needed.
  • Optional: If the target VM is located on a remote host, set up your libvirt and SSH for more convenient access to remote hosts.

Procedure

  • To connect to a local VM, use the following command and replace guest-name with the name of the VM you want to connect to: 

    # virt-viewer guest-name

  • To connect to a remote VM, use the virt-viewer command with the SSH protocol. For example, the following command connects as root to a VM called guest-name, located on remote system 10.0.0.1. The connection also requires root authentication for 10.0.0.1. 

    # virt-viewer --direct --connect qemu+ssh://root@10.0.0.1/system guest-name
root@10.0.0.1's password:

If the connection works correctly, the VM display is shown in the Virt Viewer window.

Virt Viewer displaying a RHEL 7 guest OS

You can interact with the VM console using the mouse and keyboard in the same manner you interact with a real machine. The display in the VM console reflects the activities being performed on the VM.

Additional resources

2.4.3. Connecting to a virtual machine using SSH

To interact with the terminal of a virtual machine (VM) using the SSH connection protocol, follow the procedure below:

Prerequisites

  • You have network connection and root access privileges to the target VM.
  • If the target VM is located on a remote host, you also have connection and root access privileges to that host.

  • The libvirt-nss component is installed and enabled on the VM’s host. If it is not, do the following:

    1. Install the libvirt-nss package: 

      # yum install libvirt-nss

    2. Edit the /etc/nsswitch.conf file and add libvirt_guest to the hosts line: 

      [...]
passwd:      compat
shadow:      compat
group:       compat
hosts:       files libvirt_guest dns
[...]

Procedure

  1. Optional: When connecting to a remote VM, SSH into its physical host first. The following example demonstrates connecting to a host machine 10.0.0.1 using its root credentials: 

    # ssh root@10.0.0.1
root@10.0.0.1's password:
Last login: Mon Sep 24 12:05:36 2018
root~#

  2. Use the VM’s name and user access credentials to connect to it. For example, the following connects to to the "testguest1" VM using its root credentials: 

    # ssh root@testguest1
root@testguest1's password:
Last login: Wed Sep 12 12:05:36 2018
root~]#

Troubleshooting

  • If you do not know the VM’s name, you can list all VMs available on the host using the virsh list --all command: 

    # virsh list --all
Id    Name                           State
----------------------------------------------------
2     testguest1                    running
-     testguest2                    shut off

2.4.4. Opening a virtual machine serial console

Using the virsh console command, it is possible to connect to the serial console of a virtual machine (VM).

This is useful when the VM:

  • Does not provide VNC or SPICE protocols, and thus does not offer video display for GUI tools.
  • Does not have a network connection, and thus cannot be interacted with using SSH.

Prerequisites

  • The VM must have the serial console configured in its kernel command line. To verify this, the cat /proc/cmdline command output on the VM should include console=ttyS0. For example: 

    # cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-3.10.0-948.el7.x86_64 root=/dev/mapper/rhel-root ro console=tty0 console=ttyS0,9600n8 rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb

    If the serial console is not set up properly on a VM, using virsh console to connect to the VM connects you to an unresponsive guest console. However, you can still exit the unresponsive console by using the Ctrl+] shortcut.

  • To set up serial console on the VM, do the following:

    1. On the VM, edit the /etc/default/grub file and add console=ttyS0 to the line that starts with GRUB_CMDLINE_LINUX.

    2. Clear the kernel options that may prevent your changes from taking effect. 

      # grub2-editenv - unset kernelopts

    3. Reload the Grub configuration: 

      # grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-948.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-948.el7.x86_64.img
[...]
done
    4. Reboot the VM.

Procedure

  1. On your host system, use the virsh console command. The following example connects to the guest1 VM, if the libvirt driver supports safe console handling: 

    # virsh console guest1 --safe
Connected to domain guest1
Escape character is ^]

Subscription-name
Kernel 3.10.0-948.el7.x86_64 on an x86_64

localhost login:
  2. You can interact with the virsh console in the same way as with a standard command-line interface.

Additional resources

  • For more information about the VM serial console, see the virsh man page.

2.4.5. Setting up easy access to remote virtualization hosts

When managing VMs on a remote host system using libvirt utilities, it is recommended to use the -c qemu+ssh://root@hostname/system syntax. For example, to use the virsh list command as root on the 10.0.0.1 host: 

# virsh -c qemu+ssh://root@10.0.0.1/system list

root@10.0.0.1's password:
Last login: Mon Feb 18 07:28:55 2019

Id   Name              State
---------------------------------
1    remote-guest      running

However, for convenience, you can remove the need to specify the connection details in full by modifying your SSH and libvirt configuration. For example, you will be able to do: 

# virsh -c remote-host list

root@10.0.0.1's password:
Last login: Mon Feb 18 07:28:55 2019

Id   Name              State
---------------------------------
1    remote-guest      running

To enable this improvement, follow the instructions below.

Procedure

  1. Edit or create the ~/.ssh/config file and add the following to it, where host-alias is a shortened name associated with a specific remote host, and hosturl is the URL address of the host. 

    Host host-alias
        User                    root
        Hostname                hosturl

    For example, the following sets up the tyrannosaurus alias for root@10.0.0.1: 

    Host tyrannosaurus
        User                    root
        Hostname                10.0.0.1

  2. Edit or create the /etc/libvirt/libvirt.conf file, and add the following, where qemu-host-alias is a host alias that QEMU and libvirt utilities will associate with the intended host: 

    uri_aliases = [
  "qemu-host-alias=qemu+ssh://host-alias/system",
]

    For example, the following uses the tyrannosaurus alias configured in the previous step to set up the t-rex alias, which stands for qemu+ssh://10.0.0.1/system: 

    uri_aliases = [
  "t-rex=qemu+ssh://tyrannosaurus/system",
]

  3. As a result, you can manage remote VMs by using libvirt-based utilities on the local system with an added -c qemu-host-alias parameter. This automatically performs the commands over SSH on the remote host.

    For example, the following lists VMs on the 10.0.0.1 remote host, the connection to which was set up as t-rex in the previous steps: 

    $ virsh -c t-rex list

root@10.0.0.1's password:
Last login: Mon Feb 18 07:28:55 2019

Id   Name              State
---------------------------------
1    velociraptor      running

  4. Optional: If you want to use libvirt utilities exclusively on a single remote host, you can also set a specific connection as the default target for libvirt-based utilities. To do so, edit the /etc/libvirt/libvirt.conf file and set the value of the uri_default parameter to qemu-host-alias. For example, the following uses the t-rex host alias set up in the previous steps as a default libvirt target. 

    # These can be used in cases when no URI is supplied by the application
# (@uri_default also prevents probing of the hypervisor driver).
#
uri_default = "t-rex"

    As a result, all libvirt-based commands will automatically be performed on the specified remote host. 

    $ virsh list
root@10.0.0.1's password:
Last login: Mon Feb 18 07:28:55 2019

Id   Name              State
---------------------------------
1    velociraptor      running

    However, this is not recommended if you also want to manage VMs on your local host or on different remote hosts.

Additional resources

2.5. Shutting down virtual machines

To shut down a running virtual machine in Red Hat Enterprise Linux 8, use the command line interface or the web console GUI.

2.5.1. Shutting down a virtual machine using the command-line interface

To shut down a responsive virtual machine (VM), do one of the following:

  • Use a shutdown command appropriate to the guest OS while connected to the guest.

  • Use the virsh shutdown command on the host:

    • If the VM is on a local host: 

      # virsh shutdown demo-guest1
Domain demo-guest1 is being shutdown

    • If the VM is on a remote host, in this example 10.0.0.1: 

      # virsh -c qemu+ssh://root@10.0.0.1/system shutdown demo-guest1

root@10.0.0.1's password:
Last login: Mon Feb 18 07:28:55 2019
Domain demo-guest1 is being shutdown

To force a guest to shut down, for example if it has become unresponsive, use the virsh destroy command on the host: 

# virsh destroy demo-guest1
Domain demo-guest1 destroyed
Note

The virsh destroy command does not actually delete or remove the VM configuration or disk images. It only destroys the running VM instance. However, in rare cases, this command may cause corruption of the VM’s file system, so using virsh destroy is only recommended if all other shutdown methods have failed.

2.5.2. Shutting down and restarting virtual machines using the web console

Using the RHEL 8 web console, you can shut down or restart running virtual machines. You can also send a non-maskable interrupt to an unresponsive virtual machine.

2.5.2.1. Shutting down virtual machines in the web console

If a virtual machine (VM) is in the running state, you can shut it down using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM you want to shut down.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Shut Down.

    The VM shuts down.

Troubleshooting

Additional resources

2.5.2.2. Restarting virtual machines using the web console

If a virtual machine (VM) is in the running state, you can restart it using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM you want to restart.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Restart.

    The VM shuts down and restarts.

Troubleshooting

Additional resources

2.5.2.3. Sending non-maskable interrupts to VMs using the web console

Sending a non-maskable interrupt (NMI) may cause an unresponsive running virtual machine (VM) to respond or shut down. For example, you can send the Ctrl+Alt+Del NMI to a VM that is not responding to standard input.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM to which you want to send an NMI.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click the Menu button ⋮ next to the Shut Down button and select Send Non-Maskable Interrupt.

    An NMI is sent to the VM.

Additional resources

2.6. Deleting virtual machines

To delete virtual machines in Red Hat Enterprise Linux 8, use the command line interface or the web console GUI.

2.6.1. Deleting virtual machines using the command line interface

To delete a virtual machine (VM), you can remove its XML configuration and associated storage files from the host using the command line. Follow the procedure below:

Prerequisites

  • Back up important data from the VM.
  • Shut down the VM.
  • Make sure no other VMs use the same associated storage.

Procedure

  • Use the virsh undefine utility.

    For example, the following command removes the guest1 VM, its associated storage volumes, and non-volatile RAM, if any. 

    # virsh undefine guest1 --remove-all-storage --nvram
Domain guest1 has been undefined
Volume 'vda'(/home/images/guest1.qcow2) removed.

Additional resources

  • For other virsh undefine arguments, use virsh undefine --help or see the virsh man page.

2.6.2. Deleting virtual machines using the web console

To delete a virtual machine (VM) and its associated storage files from the host to which the RHEL 8 web console is connected with, follow the procedure below:

Prerequisites

  • To use the web console to manage VMs, install the web console VM plug-in.
  • Back up important data from the VM.
  • Shut down the VM.
  • Make sure no other VMs use the same associated storage.

Procedure

  1. In the Virtual Machines interface, click the Menu button ⋮ of the VM that you want to delete.

    A drop down menu appears with controls for various VM operations.

    cockpit VM operations

  2. Click Delete.

    A confirmation dialog appears.

    cockpit vm delete confirm
  3. Optional: To delete all or some of the storage files associated with the VM, select the checkboxes next to the storage files you want to delete.

  4. Click Delete.

    The VM and any selected storage files are deleted.

Chapter 3. Getting started with virtualization on IBM POWER

You can use KVM virtualization when using RHEL 8 on IBM POWER8 or POWER9 hardware. However, enabling the KVM hypervisor on your system requires extra steps compared to virtualization on AMD64 and Intel64 architectures. Certain RHEL 8 virtualization features also have different or restricted functionality on IBM POWER.

Apart from the information in the following sections, using virtualization on IBM POWER works the same as on AMD64 and Intel 64. Therefore, you can see other RHEL 8 virtualization documentation for more information when using virtualization on IBM POWER.

3.1. Enabling virtualization on IBM POWER

To set up a KVM hypervisor and create virtual machines (VMs) on an IBM POWER8 or IBM POWER9 system running RHEL 8, follow the instructions below.

Prerequisites

  • RHEL 8 is installed and registered on your host machine.

  • The following minimum system resources are available:

    • 6 GB free disk space for the host, plus another 6 GB for each intended VM.
    • 2 GB of RAM for the host, plus another 2 GB for each intended VM.

  • Your CPU machine type must support IBM POWER virtualization.

    To verify this, query the platform information in your /proc/cpuinfo file. 

    # grep ^platform /proc/cpuinfo/
platform        : PowerNV

    If the output of this command includes the PowerNV entry, you are running a PowerNV machine type and can use virtualization on IBM POWER.

Procedure

  1. Load the KVM-HV kernel module 

    # modprobe kvm_hv

  2. Verify that the KVM kernel module is loaded 

    # lsmod | grep kvm

    If KVM loaded successfully, the output of this command includes kvm_hv.

  3. Install the packages in the virtualization module: 

    # yum module install virt

  4. Install the virt-install package: 

    # yum install virt-install

  5. Start the libvirtd service. 

    # systemctl start libvirtd

  6. Verify that your system is prepared to be a virtualization host: 

    # virt-host-validate
[...]
QEMU: Checking if device /dev/vhost-net exists                          : PASS
QEMU: Checking if device /dev/net/tun exists                            : PASS
QEMU: Checking for cgroup 'memory' controller support                   : PASS
QEMU: Checking for cgroup 'memory' controller mount-point               : PASS
[...]
QEMU: Checking for cgroup 'blkio' controller support                    : PASS
QEMU: Checking for cgroup 'blkio' controller mount-point                : PASS
QEMU: Checking if IOMMU is enabled by kernel                            : PASS

  7. If all virt-host-validate checks return a PASS value, your system is prepared for creating VMs.

    If any of the checks return a FAIL value, follow the displayed instructions to fix the problem.

    If any of the checks return a WARN value, consider following the displayed instructions to improve virtualization capabilities.

Additional information

  • Note that if virtualization is not supported by your host CPU, virt-host-validate generates the following output: 

    QEMU: Checking for hardware virtualization: FAIL (Only emulated CPUs are available, performance will be significantly limited)

    However, attempting to create VMs on such a host system will fail, rather than have performance problems.

3.2. How virtualization on IBM POWER differs from AMD64 and Intel 64

KVM virtualization in RHEL 8 on IBM POWER systems is different from KVM on AMD64 and Intel 64 systems in a number of aspects, notably:

Memory requirements
VMs on IBM POWER consume more memory. Therefore, the recommended minimum memory allocation for a virtual machine (VM) on an IBM POWER host is 2GB RAM.
Display protocols

The SPICE protocol is not supported on IBM POWER systems. To display the graphical output of a VM, use the VNC protocol. In addition, only the following virtual graphics card devices are supported:

  • vga - only supported in -vga std mode and not in -vga cirrus mode.
  • virtio-vga
  • virtio-gpu
SMBIOS
SMBIOS configuration is not available.
Memory allocation errors

POWER8 VMs, including compatibility mode VMs, may fail with an error similar to: 

qemu-kvm: Failed to allocate KVM HPT of order 33 (try smaller maxmem?): Cannot allocate memory

This is significantly more likely to occur on VMs that use RHEL 7.3 and prior as the guest OS.

To fix the problem, increase the CMA memory pool available for the guest’s hashed page table (HPT) by adding kvm_cma_resv_ratio=memory to the host’s kernel command line, where memory is the percentage of the host memory that should be reserved for the CMA pool (defaults to 5).

Huge pages

Transparent huge pages (THPs) do not provide any notable performance benefits on IBM POWER8 VMs. However, IBM POWER9 VMs can benefit from THPs as expected.

In addition, the size of static huge pages on IBM POWER8 systems are 16 MiB and 16 GiB, as opposed to 2 MiB and 1 GiB on AMD64, Intel 64, and IBM POWER9. As a consequence, to migrate a VM configured with static huge pages from an IBM POWER8 host to an IBM POWER9 host, you must first set up 1GiB huge pages on the VM.

kvm-clock
The kvm-clock service does not have to be configured for time management in VMs on IBM POWER9.
pvpanic

IBM POWER9 systems do not support the pvpanic device. However, an equivalent functionality is available and activated by default on this architecture. To enable it in a VM, use the <on_crash> XML configuration element with the preserve value.

In addition, make sure to remove the <panic> element from the <devices> section, as its presence can lead to the VM failing to boot on IBM POWER systems.

Single-threaded host
On IBM POWER8 systems, the host machine must run in single-threaded mode to support VMs. This is automatically configured if the qemu-kvm packages are installed. However, VMs running on single-threaded hosts can still use multiple threads.
Peripheral devices

A number of peripheral devices supported on AMD64 and Intel 64 systems are not supported on IBM POWER systems, or a different device is supported as a replacement.

  • Devices used for PCI-E hierarchy, including ioh3420 and xio3130-downstream, are not supported. This functionality is replaced by multiple independent PCI root bridges provided by the spapr-pci-host-bridge device.
  • UHCI and EHCI PCI controllers are not supported. Use OHCI and XHCI controllers instead.
  • IDE devices, including the virtual IDE CD-ROM (ide-cd) and the virtual IDE disk (ide-hd), are not supported. Use the virtio-scsi and virtio-blk devices instead.
  • Emulated PCI NICs (rtl8139) are not supported. Use the virtio-net device instead.
  • Sound devices, including intel-hda, hda-output, and AC97, are not supported.
  • USB redirection devices, including usb-redir and usb-tablet, are not supported.
v2v and p2v
The virt-v2v and virt-p2v utilities are supported only on the AMD64 and Intel 64 architecture, and are not provided on IBM POWER.

Additional sources

Chapter 4. Getting started with virtualization on IBM Z

You can use KVM virtualization when using RHEL 8 on IBM Z hardware. However, enabling the KVM hypervisor on your system requires extra steps compared to virtualization on AMD64 and Intel 64 architectures. Certain RHEL 8 virtualization features also have different or restricted functionality on IBM Z.

Apart from the information in the following sections, using virtualization on IBM Z works the same as on AMD64 and Intel 64. Therefore, you can see other RHEL 8 virtualization documentation for more information when using virtualization on IBM Z.

4.1. Enabling virtualization on IBM Z

To set up a KVM hypervisor and create virtual machines (VMs) on an IBM Z system running RHEL 8, follow the instructions below.

Prerequisites

  • RHEL 8 is installed and registered on your host machine.

  • The following minimum system resources are available:

    • 6 GB free disk space for the host, plus another 6 GB for each intended VM.
    • 2 GB of RAM for the host, plus another 2 GB for each intended VM.
  • Your IBM Z host system is using a z13 CPU or later.

  • RHEL 8 is installed on a logical partition (LPAR). In addition, the LPAR supports the start-interpretive execution (SIE) virtualization functions.

    To verify this, search for sie in your /proc/cpuinfo file. 

    # grep sie /proc/cpuinfo/
features        : esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs te sie

Procedure

  1. Load the KVM kernel module: 

    # modprobe kvm

  2. Verify that the KVM kernel module is loaded: 

    # lsmod | grep kvm

    If KVM loaded successfully, the output of this command includes kvm:

  3. Install the packages in the virtualization module: 

    # yum module install virt

  4. Install the virt-install package: 

    # yum install virt-install

  5. Start the libvirtd service. 

    # systemctl start libvirtd

  6. Verify that your system is prepared to be a virtualization host: 

    # virt-host-validate
[...]
QEMU: Checking if device /dev/kvm is accessible                : PASS
QEMU: Checking if device /dev/vhost-net exists                 : PASS
QEMU: Checking if device /dev/net/tun exists                   : PASS
QEMU: Checking for cgroup 'memory' controller support          : PASS
QEMU: Checking for cgroup 'memory' controller mount-point      : PASS
[...]

  7. If all virt-host-validate checks return a PASS value, your system is prepared for creating VMs.

    If any of the checks return a FAIL value, follow the displayed instructions to fix the problem.

    If any of the checks return a WARN value, consider following the displayed instructions to improve virtualization capabilities.

Additional information

  • Note that if virtualization is not supported by your host CPU, virt-host-validate generates the following output: 

    QEMU: Checking for hardware virtualization: FAIL (Only emulated CPUs are available, performance will be significantly limited)

    However, attempting to create VMs on such a host system will fail, rather than have performance problems.

4.2. How virtualization on IBM Z differs from AMD64 and Intel 64

KVM virtualization in RHEL 8 on IBM Z systems differs from KVM on AMD64 and Intel 64 systems in the following:

No graphical output
Displaying the VM graphical output is not possible when connecting to the VM using the VNC protocol. This is because the gnome-desktop utility is not supported on IBM Z. In addition, the SPICE display protocol does not work on IBM Z.
PCI and USB devices

Virtual PCI and USB devices are not supported on IBM Z. This also means that virtio-*-pci devices are unsupported, and virtio-*-ccw devices should be used instead. For example, use virtio-net-ccw instead of virtio-net-pci.

Note that direct attachment of PCI devices, also known as PCI passthrough, is supported.

Supported guest OS
Red Hat only supports VMs hosted on IBM Z if they use RHEL 7 or RHEL 8 as their guest operating system.
Device boot order

IBM Z does not support the <boot dev='device'> XML configuration element. To define device boot order, use the <boot order='number'> element in the <devices> section of the XML. For example: 

<disk type='file' device='disk'>
  <driver name='qemu' type='qcow2'/>
  <source file='/path/to/qcow2'/>
  <target dev='vda' bus='virtio'/>
  <address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0000'/>
  <boot order='2'>
</disk>
Note

Using <boot order='number'> for boot order management is also preferred on AMD64 and Intel 64 hosts.

Memory hot plug
Adding memory to a running VM is not possible on IBM Z. Note that removing memory from a running VM (memory hot unplug) is also not possible on IBM Z, as well as on AMD64 and Intel 64.
NUMA topology
Non-Uniform Memory Access (NUMA) topology for CPUs is not supported by libvirt on IBM Z. Therefore, tuning vCPU performance using NUMA is not possible on these systems.
vfio-ap
VMs on an IBM Z host can use the vfio-ap cryptographic device passthrough, which is not supported on any other architectures.
SMBIOS
SMBIOS configuration is not available on IBM Z.
Watchdog devices

If using watchdog devices in your VM on an IBM Z host, use the diag288 model. For example: 

<devices>
  <watchdog model='diag288' action='poweroff'/>
</devices>
kvm-clock
The kvm-clock service is specific to AMD64 and Intel 64 systems, and does not have to be configured for VM time management on IBM Z.
v2v and p2v
The virt-v2v and virt-p2v utilities are supported only on the AMD64 and Intel 64 architecture, and are not provided on IBM Z.
Nested virtualization
Creating nested VMs requires different settings on IBM Z than on AMD64 and Intel 64. For details, see Chapter 18, Creating nested virtual machines.

Additional sources

Chapter 5. Managing virtual machines in the web console

Manage your virtual machines in a RHEL 8 web console and learn about the virtualization management capabilities.

To manage virtual machines in a graphical interface on a RHEL 8 host, you can use the Virtual Machines pane in the RHEL 8 web console.

web console overview

5.1. Overview of virtual machine management using the web console

The RHEL 8 web console is a web-based interface for system administration. As one of its features, the web console provides a graphical view of virtual machines (VMs) on the host system, and makes it possible to create, access, and configure these VMs.

Note that to use the web console to manage your VMs on RHEL 8, you must first install a web console plug-in for virtualization.

Next steps

5.2. Setting up the web console to manage virtual machines

Before using the RHEL 8 web console to manage virtual machines (VMs), you must install the web console virtual machine plug-in on the host.

Prerequisites

  • Ensure that the web console is installed and enabled on your machine. 

    # systemctl status cockpit.socket
cockpit.socket - Cockpit Web Service Socket
Loaded: loaded (/usr/lib/systemd/system/cockpit.socket
[...]

    If this command returns Unit cockpit.socket could not be found, follow the Installing the web console document to enable the web console.

Procedure

  • Install the cockpit-machines plug-in. 

    # yum install cockpit-machines

Verification

  • If the installation is successful, Virtual Machines appears in the web console side menu.

    cockpit vms info

Additional resources

5.3. Virtual machine management features available in the web console

Using the RHEL 8 web console, you can perform the following actions to manage the virtual machines (VMs) on your system.

5.4. Differences between virtualization features in Virtual Machine Manager and the web console

The Virtual Machine Manager (virt-manager) application is supported in RHEL 8, but has been deprecated. The web console is intended to become its replacement in a subsequent major release. It is, therefore, recommended that you get familiar with the web console for managing virtualization in a GUI.

However, in RHEL 8, some VM management tasks can only be performed in virt-manager or the command line. The following table highlights the features that are available in virt-manager but not available in the RHEL 8.0 web console.

If a feature is available in a later minor version of RHEL 8, the minimum RHEL 8 version appears in the Support in web console introduced column.

Table 5.2. VM managemennt tasks that cannot be performed using the web console in RHEL 8.0

TaskSupport in web console introducedAlternative method using CLI

Setting a virtual machine to start when the host boots

RHEL 8.1

virsh autostart

Suspending a virtual machine

RHEL 8.1

virsh suspend

Resuming a suspended virtual machine

RHEL 8.1

virsh resume

Creating file-system directory storage pools

RHEL 8.1

virsh pool-define-as

Creating NFS storage pools

RHEL 8.1

virsh pool-define-as

Creating physical disk device storage pools

RHEL 8.1

virsh pool-define-as

Creating LVM volume group storage pools

RHEL 8.1

virsh pool-define-as

Creating partition-based storage pools

CURRENTLY UNAVAILABLE

virsh pool-define-as

Creating GlusterFS-based storage pools

CURRENTLY UNAVAILABLE

virsh pool-define-as

Creating vHBA-based storage pools with SCSI devices

CURRENTLY UNAVAILABLE

virsh pool-define-as

Creating Multipath-based storage pools

CURRENTLY UNAVAILABLE

virsh pool-define-as

Creating RBD-based storage pools

CURRENTLY UNAVAILABLE

virsh pool-define-as

Creating a new storage volume

RHEL 8.1

virsh vol-create

Adding a new virtual network

RHEL 8.1

virsh net-create or virsh net-define

Deleting a virtual network

RHEL 8.1

virsh net-undefine

Creating a bridge from a host machine’s interface to a virtual machine

CURRENTLY UNAVAILABLE

virsh iface-bridge

Creating a snapshot

CURRENTLY UNAVAILABLE

virsh snapshot-create-as

Reverting to a snapshot

CURRENTLY UNAVAILABLE

virsh snapshot-revert

Deleting a snapshot

CURRENTLY UNAVAILABLE

virsh snapshot-delete

Cloning a virtual machine

CURRENTLY UNAVAILABLE

virt-clone

Migrating a virtual machine to another host machine

CURRENTLY UNAVAILABLE

virsh migrate

Additional resources

Chapter 6. Viewing information about virtual machines

When you need to adjust or troubleshoot any aspect of your virtualization deployment on RHEL 8, the first step you need to perform usually is to view information about the current state and configuration of your virtual machines. To do so, you can use the command-line interface or the web console. You can also view the information in the VM’s XML configuration.

6.1. Viewing virtual machine information using the command-line interface

To retrieve information about virtual machines (VMs) on your host and their configurations, use one or more of the following commands.

Procedure

  • To obtain a list of VMs on your host: 

    # virsh list --all
Id   Name              State
----------------------------------
1    testguest1             running
-    testguest2             shut off
-    testguest3             shut off
-    testguest4             shut off

  • To obtain basic information about a specific VM: 

    # virsh dominfo testguest1
Id:             1
Name:           testguest1
UUID:           a973666f-2f6e-415a-8949-75a7a98569e1
OS Type:        hvm
State:          running
CPU(s):         2
CPU time:       188.3s
Max memory:     4194304 KiB
Used memory:    4194304 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: selinux
Security DOI:   0
Security label: system_u:system_r:svirt_t:s0:c486,c538 (enforcing)

  • To obtain the complete XML configuration of a specific VM: 

    # virsh dumpxml testguest2

<domain type='kvm' id='1'>
  <name>testguest2</name>
  <uuid>a973434f-2f6e-4ěša-8949-76a7a98569e1</uuid>
  <metadata>
[...]

  • For information about a VM’s disks and other block devices: 

    # virsh domblklist testguest3
 Target   Source
---------------------------------------------------------------
 vda      /var/lib/libvirt/images/testguest3.qcow2
 sda      -
 sdb      /home/username/Downloads/virt-p2v-1.36.10-1.el7.iso

    For instructions on managing a VM’s storage, see Chapter 11, Managing storage for virtual machines.

  • To obtain information about a VM’s file systems and their mountpoints: 

    # virsh domfsinfo testguest3
Mountpoint   Name   Type   Target
------------------------------------
 /            dm-0   xfs
 /boot        vda1   xfs

  • To obtain more details about the vCPUs of a specific VM: 

    # virsh vcpuinfo testguest4
VCPU:           0
CPU:            3
State:          running
CPU time:       103.1s
CPU Affinity:   yyyy

VCPU:           1
CPU:            0
State:          running
CPU time:       88.6s
CPU Affinity:   yyyy

    To configure and optimize the vCPUs in your VM, see Section 16.5, “Optimizing virtual machine CPU performance”.

  • To list all virtual network interfaces on your host: 

    # virsh net-list --all
 Name       State    Autostart   Persistent
---------------------------------------------
 default    active   yes         yes
 labnet     active   yes         yes

    For information about a specific interface: 

    # virsh net-info default
Name:           default
UUID:           c699f9f6-9202-4ca8-91d0-6b8cb9024116
Active:         yes
Persistent:     yes
Autostart:      yes
Bridge:         virbr0

    For details about network interfaces, VM networks, and instructions for configuring them, see Chapter 13, Configuring virtual machine network connections.

  • For instructions on viewing information about storage pools and storage volumes on your host, see Section 11.2.1, “Viewing virtual machine storage information using the CLI”.

6.2. Viewing virtual machine information using the web console

Using the RHEL 8 web console, you can view information about the virtual storage and VMs to which the web console is connected.

6.2.1. Viewing a virtualization overview in the web console

The following procedure describes how to view an overview of virtual machines (VMs) and the available virtual storage to which the web console session is connected.

Prerequisites

Procedure

  • Click Virtual Machines in the web console’s side menu.

    A dialog box appears with information about the available storage and the VMs to which the web console is connected.

cockpit vms info

The information includes the following:

  • Storage Pools - The number of storage pools that can be accessed by the web console and their state.
  • Networks - The number of networks that can be accessed by the web console and their state.
  • Name - The name of the VM.
  • Connection - The type of libvirt connection, system or session.
  • State - The state of the VM.

Additional resources

6.2.2. Viewing storage pool information using the web console

The following procedure describes how to view detailed storage pool information about the virtual machine (VM) storage pools that the web console session can access.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines interface. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

    The information includes the following:

    • Name - The name of the storage pool.
    • Size - The size of the storage pool.
    • Connection - The connection used to access the storage pool.
    • State - The state of the storage pool.

  2. Click the row of the storage whose information you want to see.

    The row expands to reveal the Overview pane with the following information about the selected storage pool:

    • Path - The path to the storage pool.
    • Persistent - Whether or not the storage pool is persistent.
    • Autostart - Whether or not the storage pool starts automatically.
    • Type - The type of the storage pool.
    web console storage pool overview

  3. To view a list of storage volumes created from the storage pool, click Storage Volumes.

    The Storage Volumes pane appears, showing a list of configured storage volumes with their sizes and the amount of space used.

    web console storage pool storage volumes

Additional resources

6.2.3. Viewing basic virtual machine information in the web console

The following describes how to view basic information about a selected virtual machine (VM) to which the web console session is connected.

Prerequisites

Procedure

  1. Click Virtual Machines in the web console side menu.

  2. Click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  3. If another tab is selected, click Overview.

    cockpit basic vm info

The information includes the following general VM details:

  • Memory - The amount of memory assigned to the VM.
  • vCPUs - The number of virtual CPUs configured for the VM.
  • CPU Type - The architecture of the virtual CPUs configured for the VM.
  • Boot Order - The boot order configured for the VM.
  • Autostart - Whether or not autostart is enabled for the VM.

The information also includes the following hypervisor details:

  • Emulated Machine - The machine type emulated by the VM.
  • Firmware - The firmware of the VM.

Additional resources

6.2.4. Viewing virtual machine resource usage in the web console

The following procedure describes how to view the memory and virtual CPU usage information about a selected virtual machine (VM) to which the web console session is connected.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Usage.

    The Usage pane appears with information about the memory and virtual CPU usage of the VM.

cockpit resource usage

Additional resources

6.2.5. Viewing virtual machine disk information in the web console

The following procedure describes how to view the disk information of a virtual machine (VM) to which the web console session is connected.

Prerequisites

To use the web console to manage VMs, install the web console VM plug-in.

Procedure

  1. Click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Disks.

    The Disks pane appears with information about the disks assigned to the VM.

cockpit disk info

The information includes the following:

  • Device - The device type of the disk.
  • Used - The amount of the disk that is used.
  • Capacity - The size of the disk.
  • Bus - The bus type of the disk.
  • Access - Whether the disk is is writeable or read-only.
  • Source - The disk device or file.

Additional resources

6.2.6. Viewing and editing virtual network interface information in the web console

Using the RHEL 8 web console, you can view and modify the virtual network interfaces on a selected virtual machine (VM):

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Network Interfaces.

    The Networks Interfaces pane appears with information about the virtual network interface configured for the VM.

    cockpit vNIC info

    The information includes the following:

    • Type - The type of network interface for the VM. Types include virtual network, bridge to LAN, and direct attachment.

      Note

      Generic Ethernet connection is not supported in RHEL 8.2.

    • Model type - The model of the virtual network interface.
    • MAC Address - The MAC address of the virtual network interface.
    • IP Address - The IP address of the virtual network interface.
    • Source - The source of the network interface. This is dependent on the network type.
    • State - The state of the virtual network interface.

  3. To edit the virtual network interface settings, Click Edit. The Virtual Network Interface Settings dialog opens.

    web console virtual network if settings
  4. Change the interface type, source, or model.

  5. Click Save. The network interface is modified.

    Note

    Changes to the virtual network interface settings take effect only after restarting the VM.

Additional resources

6.3. Sample virtual machine XML configuration

The XML configuration of a VM, also referred to as a domain XML, determines the VM’s settings and components. The following table shows sections of a sample XML configuration of a virtual machine (VM) and explains the contents.

To obtain the XML configuration of a VM, you can use the virsh dumpxml command followed by the VM’s name. 

# virsh dumpxml testguest1

Table 6.1. Sample XML configuration

Domain XML SectionDescription
<domain type='kvm'>
 <name>Testguest1</name>
 <uuid>ec6fbaa1-3eb4-49da-bf61-bb02fbec4967</uuid>
 <memory unit='KiB'>1048576</memory>
 <currentMemory unit='KiB'>1048576</currentMemory>

This is a KVM virtual machine called Testguest1, with 1024 MiB allocated RAM. 

 <vcpu placement='static'>1</vcpu>

The VM is allocated with a single virtual CPU (vCPU).

For information about configuring vCPUs, see Section 16.5, “Optimizing virtual machine CPU performance”. 

 <os>
  <type arch='x86_64' machine='pc-q35-4.1'>hvm</type>
  <boot dev='hd'/>
 </os>

The machine architecture is set to the AMD64 and Intel 64 architecture, and uses the Intel Q35 machine type to determine feature compatibility. The OS is set to be booted from the hard drive.

For information about creating a VM with an installed OS, see Section 2.2.2, “Creating virtual machines and installing guest operating systems using the web console”. 

 <features>
  <acpi/>
  <apic/>
  <vmport state='off'/>
 </features>

The acpi and apic hypervisor features are disabled and the VMWare IO port is turned off. 

 <cpu mode='host-model' check='partial'>

The host CPU definitions from capabilities XML (obtainable with virsh capabilities) are automatically copied into the VM’s XML configuration. Therefore, when the VM is booted, libvirt picks a CPU model that is similar to the host CPU, and then adds extra features to approximate the host model as closely as possible. 

 <clock offset='utc'>
  <timer name='rtc' tickpolicy='catchup'/>
  <timer name='pit' tickpolicy='delay'/>
  <timer name='hpet' present='no'/>
 </clock>

The VM’s virtual hardware clock uses the UTC time zone. In addition, three different timers are set up for synchronization with the QEMU hypervisor. 

 <on_poweroff>destroy</on_poweroff>
 <on_reboot>restart</on_reboot>
 <on_crash>destroy</on_crash>

When the VM powers off, or its OS terminates unexpectedly, libvirt terminates the VM and releases all its allocated resources. When the VM is rebooted, libvirt restarts it with the same configuration. 

 <pm>
  <suspend-to-mem enabled='no'/>
  <suspend-to-disk enabled='no'/>
 </pm>

The S3 and S4 ACPI sleep states are disabled for this VM. 

 <devices>
  <emulator>/usr/bin/qemu-kvm</emulator>
  <disk type='file' device='disk'>
   <driver name='qemu' type='qcow2'/>
   <source file='/var/lib/libvirt/images/Testguest.qcow2'/>
   <target dev='hda' bus='ide'/>
   <address type='drive' controller='0' bus='0' target='0' unit='0'/>
  </disk>
  <disk type='file' device='cdrom'>
   <driver name='qemu' type='raw'/>
   <target dev='hdb' bus='ide'/>
   <readonly/>
   <address type='drive' controller='0' bus='0' target='0' unit='1'/>
  </disk>

The VM uses the /usr/bin/qemu-kvm binary file for emulation. In addition, it has two disks attached. The first disk is a virtualized hard-drive based on the /var/lib/libvirt/images/Testguest.qcow2 stored on the host, and its logical device name is set to hda. 

  <controller type='usb' index='0' model='qemu-xhci' ports='15'>
   <address type='pci' domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
  </controller>
  <controller type='sata' index='0'>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
  </controller>
  <controller type='pci' index='0' model='pcie-root'/>
  <controller type='pci' index='1' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='1' port='0x10'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0' multifunction='on'/>
  </controller>
  <controller type='pci' index='2' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='2' port='0x11'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x1'/>
  </controller>
  <controller type='pci' index='3' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='3' port='0x12'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x2'/>
  </controller>
  <controller type='pci' index='4' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='4' port='0x13'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x3'/>
  </controller>
  <controller type='pci' index='5' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='5' port='0x14'/>
     <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x4'/>
  </controller>
  <controller type='pci' index='6' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='6' port='0x15'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x5'/>
  </controller>
  <controller type='pci' index='7' model='pcie-root-port'>
   <model name='pcie-root-port'/>
   <target chassis='7' port='0x16'/>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x6'/>
  </controller>
  <controller type='virtio-serial' index='0'>
   <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
  </controller>

The VM uses a single controller for attaching USB devices, and a root controller for PCI-Express (PCIe) devices. In addition, a virtio-serial controller is available, which enables the VM to interact with the host in a variety of ways, such as the serial console.

For more information about virtual devices, see Section 10.5, “Types of virtual devices”. 

 <interface type='network'>
  <mac address='52:54:00:65:29:21'/>
  <source network='default'/>
  <model type='rtl8139'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
 </interface>

A network interface is set up in the VM that uses the default virtual network and the rtl8139 network device model.

For information about configuring the network interface, see Section 16.6, “Optimizing virtual machine network performance”. 

  <serial type='pty'>
   <target type='isa-serial' port='0'>
    <model name='isa-serial'/>
   </target>
  </serial>
  <console type='pty'>
   <target type='serial' port='0'/>
  </console>
  <channel type='unix'>
   <target type='virtio' name='org.qemu.guest_agent.0'/>
   <address type='virtio-serial' controller='0' bus='0' port='1'/>
  </channel>
  <channel type='spicevmc'>
   <target type='virtio' name='com.redhat.spice.0'/>
    <address type='virtio-serial' controller='0' bus='0' port='2'/>
  </channel>

A pty serial console is set up on the VM, which enables rudimentary VM communication with the host. The console uses the UNIX channel on port 1, and the paravirtualized SPICE on port 2. This is set up automatically and changing these settings is not recommended.

For more information about interacting with VMs, see Section 2.4.1, “Interacting with virtual machines using the web console”. 

  <input type='tablet' bus='usb'>
   <address type='usb' bus='0' port='1'/>
  </input>
  <input type='mouse' bus='ps2'/>
  <input type='keyboard' bus='ps2'/>

The VM uses a virtual usb port, which is set up to receive tablet input, and a virtual ps2 port set up to receive mouse and keyboard input. This is set up automatically and changing these settings is not recommended. 

  <graphics type='spice' autoport='yes' listen='127.0.0.1'>
   <listen type='address' address='127.0.0.1'/>
   <image compression='off'/>
  </graphics>
  <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
   <listen type='address' address='127.0.0.1'/>
  </graphics>

The VM uses the vnc and SPICE protocols for rendering its graphical output, and image compression is turned off. 

  <sound model='ich6'>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
  </sound>
  <video>
   <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
  </video>

An ICH6 HDA sound device is set up for the VM, and the QEMU QXL paravirtualized framebuffer device is set up as the video accelerator. This is set up automatically and changing these settings is not recommended. 

  <redirdev bus='usb' type='spicevmc'>
   <address type='usb' bus='0' port='1'/>
  </redirdev>
  <redirdev bus='usb' type='spicevmc'>
   <address type='usb' bus='0' port='2'/>
  </redirdev>
  <memballoon model='virtio'>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
  </memballoon>
 </devices>
</domain>

The VM has two re-directors for attaching USB devices remotely, and memory ballooning is turned on. This is set up automatically and changing these settings is not recommended.

Chapter 7. Saving and restoring virtual machines

To free up system resources, you can shut down a virtual machine (VM) running on that system. However, when you require the VM again, you must boot up the guest operating system (OS) and restart the applications, which may take a considerable amount of time. To reduce this downtime and enable the VM workload to start running sooner, you can use the save and restore feature to avoid the OS shutdown and boot sequence entirely.

This section provides information about saving VMs, as well as about restoring them to the same state without a full VM boot-up.

7.1. How saving and restoring virtual machines works

Saving a virtual machine (VM) saves its memory and device state to the host’s disk, and immediately stops the VM process. You can save a VM that is either in a running or paused state, and upon restoring, the VM will return to that state.

This process frees up RAM and CPU resources on the host system in exchange for disk space, which may improve the host system performance. When the VM is restored, because the guest OS does not need to be booted, the long boot-up period is avoided as well.

To save a VM, you can use the command-line interface (CLI). For instructions, see Saving virtual machines using the command line interface.

To restore a VM you can use the CLI or the web console GUI.

7.2. Saving a virtual machine using the command line interface

To save a virtual machine (VM) using the command line, follow the procedure below.

Prerequisites

  • Make sure you have sufficient disk space to save the VM and its configuration. Note that the space occupied by the VM depends on the amount of RAM allocated to that VM.
  • Make sure the VM is persistent.
  • Optional: Back up important data from the VM if required.

Procedure

  • Use the virsh managedsave utility.

    For example, the following command stops the demo-guest1 VM and saves its configuration. 

    # virsh managedsave demo-guest1
Domain demo-guest1 saved by libvirt

    The saved VM file is located by default in the /var/lib/libvirt/qemu/save directory as demo-guest1.save.

    The next time the VM is started, it will automatically restore the saved state from the above file.

Verification

  • You can make sure that the VM is in a saved state or shut off using the virsh list utility.

    To list the VMs that have managed save enabled, use the following command. The VMs listed as saved have their managed save enabled. 

    # virsh list --managed-save --all
Id    Name                           State
----------------------------------------------------
-     demo-guest1                    saved
-     demo-guest2                    shut off

    To list the VMs that have a managed save image: 

    # virsh list --with-managed-save --all
Id    Name                           State
----------------------------------------------------
-     demo-guest1                    shut off

    Note that to list the saved VMs that are in a shut off state, you must use the --all or --inactive options with the command.

Troubleshooting

  • If the saved VM file becomes corrupted or unreadable, restoring the VM will initiate a standard VM boot instead.

Additional resources

7.3. Starting a virtual machine using the command-line interface

You can use the command line interface to start a shutdown virtual machine (VM) or restore a saved VM. Follow the procedure below.

Prerequisites

  • An inactive VM that is already defined.
  • The name of the VM.

  • For remote VMs:

    • The IP address of the host where the VM is located.
    • Root access privileges to the host.

Procedure

  • For a local VM, use the virsh start utility.

    For example, the following command starts the demo-guest1 VM. 

    # virsh start demo-guest1
Domain demo-guest1 started

  • For a VM located on a remote host, use the virsh start utility along with the QEMU+SSH connection to the host.

    For example, the following command starts the demo-guest1 VM on the 192.168.123.123 host. 

    # virsh -c qemu+ssh://root@192.168.123.123/system start demo-guest1

root@192.168.123.123's password:
Last login: Mon Feb 18 07:28:55 2019

Domain demo-guest1 started

Additional Resources

  • For more virsh start arguments, use virsh start --help.
  • For simplifying VM management on remote hosts, see modifying your libvirt and SSH configuration.
  • You can use the virsh autostart utility to configure a VM to start automatically when the host boots up. For more information about autostart, see the virsh autostart help page.

7.4. Starting virtual machines using the web console

If a virtual machine (VM) is in the shut off state, you can start it using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM you want to start.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Run.

    The VM starts, and you can connect to its console or graphical output.

  3. Optional: To set up the VM to start automatically when the host starts, click the Autostart checkbox.

Additional resources

Chapter 8. Cloning virtual machines

To quickly create a new virtual machine (VM) with a specific set of properties, you can clone an existing VM.

Cloning creates a new VM that uses its own disk image for storage, but most of the clone’s configuration and stored data is identical to the source VM. This makes it possible to prepare a number of VMs optimized for a certain task without the need to optimize each VM individually.

8.1. How cloning virtual machines works

Cloning a virtual machine (VM) copies the XML configuration of the source VM and its disk images, and makes adjustments to the configurations to ensure the uniqueness of the new VM. This includes changing the name of the VM and ensuring it uses the disk image clones. Nevertheless, the data stored on the clone’s virtual disks is identical to the source VM.

This process is faster than creating a new VM and installing it with a guest operating system, and can be used to rapidly generate VMs with a specific configuration and content.

If you are planning to create multiple clones of a VM, first create a VM template that does not contain:

  • Unique settings, such as persistent network MAC configuration, which can prevent the clones from working correctly.
  • Sensitive data, such as SSH keys and password files.

For instructions, see Section 8.2, “Creating a virtual machine template”.

To clone a VM, you can use the RHEL 8 CLI. For details, see Section 8.3, “Cloning a virtual machine using the command-line interface”.

8.2. Creating a virtual machine template

To ensure that the virtual machine (VM) clones run correctly, remove information and configurations that are unique to the source VM, such as SSH keys or persistent network MAC configuration, before cloning the source VM.

This creates a VM template, which can be used to easily and safely create VM clones.

Prerequisites

  • The virt-sysprep utility is installed on your host: 

    # yum install /usr/bin/virt-sysprep
  • The VM intended as a template is shut down.

  • You must know where the disk image for the source VM is located, and be the owner of the VM’s disk image file.

    Note that disk images for VMs created in the system session of libvirt are by default located in the /var/lib/libvirt/images directory and owned by the root user: 

    # ls -la /var/lib/libvirt/images
-rw-------.  1 root root  9665380352 Jul 23 14:50 a-really-important-vm.qcow2
-rw-------.  1 root root  8591507456 Jul 26  2017 an-actual-vm-that-i-use.qcow2
-rw-------.  1 root root  8591507456 Jul 26  2017 totally-not-a-fake-vm.qcow2
-rw-------.  1 root root 10739318784 Sep 20 17:57 another-vm-example.qcow2
  • Optional: Any important data on the VM’s disk has been backed up. If you want to preserve the source VM intact, clone it first and edit the clone to create a template.

Procedure

  1. Ensure you are logged in as the owner of the VM’s disk image: 

    # whoami
root

  2. Optional: Copy the disk image of the VM. 

    # cp /var/lib/libvirt/images/a-really-important-vm.qcow2 /var/lib/libvirt/images/a-really-important-vm-original.qcow2

    This is used later to verify the VM was successfully turned into a template.

  3. Use the following command, and replace /var/lib/libvirt/images/a-really-important-vm.qcow2 with the path to the disk image of the source VM. 

    # virt-sysprep -a /var/lib/libvirt/images/a-really-important-vm.qcow2
[   0.0] Examining the guest ...
[   7.3] Performing "abrt-data" ...
[   7.3] Performing "backup-files" ...
[   9.6] Performing "bash-history" ...
[   9.6] Performing "blkid-tab" ...
[...]

Verification

  • To confirm that the process was successful, compare the modified disk image to the original one. The following example shows a successful creation of a template: 

    # virt-diff -a /var/lib/libvirt/images/a-really-important-vm-orig.qcow2 -A /var/lib/libvirt/images/a-really-important-vm.qcow2
- - 0644       1001 /etc/group-
- - 0000        797 /etc/gshadow-
= - 0444         33 /etc/machine-id
[...]
- - 0600        409 /home/username/.bash_history
- d 0700          6 /home/username/.ssh
- - 0600        868 /root/.bash_history
[...]

Additional resources

  • Using the virt-sysprep command as shown above performs the standard VM template preparation. For more information, see the OPERATIONS section in the virt-sysprep man page.

    To customize which specific operations you want virt-sysprep to perform, use the --operations option, and specify the intended operations as a comma-separated list.

  • For instructions on cloning a VM template, see Section 8.3, “Cloning a virtual machine using the command-line interface”.

8.3. Cloning a virtual machine using the command-line interface

To quickly create a new virtual machine (VM) with a specific set of properties, for example for testing purposes, you can clone an existing VM. To do so using the CLI, follow the instructions below.

Prerequisites

  • The source VM is shut down.
  • Ensure that there is sufficient disk space to store the cloned disk images.
  • Optional: When creating multiple VM clones, remove unique data and settings from the source VM to ensure the cloned VMs work properly. For instructions, see Section 8.2, “Creating a virtual machine template”.

Procedure

  1. Use the virt-clone utility with options that are appropriate for your environment and use case.

    Sample use cases

    • The following command clones a local VM named doppelganger and creates the doppelganger-clone VM. It also creates the doppelganger-clone.qcow2 disk image in the same location as the disk image of the original VM, and with the same data: 

      # virt-clone --original doppelganger --auto-clone
Allocating 'doppelganger-clone.qcow2'                            | 50.0 GB  00:05:37

Clone 'doppelganger-clone' created successfully.

    • The following command clones a VM named geminus1, and creates a local VM named geminus2, which uses only two of geminus1's multiple disks. 

      # virt-clone --original geminus1 --name geminus2 --file /var/lib/libvirt/images/disk1.qcow2 --file /var/lib/libvirt/images/disk2.qcow2
Allocating 'disk1-clone.qcow2'                                      | 78.0 GB  00:05:37
Allocating 'disk2-clone.qcow2'                                      | 80.0 GB  00:05:37

Clone 'geminus2' created successfully.

    • To clone your VM to a different host, migrate the VM without undefining it on the local host. For example, the following commands clone the previously created geminus2 VM to the 10.0.0.1 remote system, including its local disks. Note that using these commands also requires root privileges for 10.0.0.1. 

      # virsh migrate --offline --persistent geminus2 qemu+ssh://root@10.0.0.1/system
root@10.0.0.1's password:

# scp /var/lib/libvirt/images/disk1-clone.qcow2 root@10.0.0.1/user@remote_host.com://var/lib/libvirt/images/

# scp /var/lib/libvirt/images/disk2-clone.qcow2 root@10.0.0.1/user@remote_host.com://var/lib/libvirt/images/

Verification

To verify the VM has been successfully cloned and is working correctly:

  1. Confirm the clone has been added to the list of VMs on your host. 

    # virsh list --all
Id   Name                  State
---------------------------------------
-    doppelganger          shut off
-    doppelganger-clone    shut off

  2. Start the clone and observe if it boots up. 

    # virsh start doppelganger-clone
Domain doppelganger-clone started

Additional resources

  • For additional options for cloning VMs, see the virt-clone man page.
  • For details on moving the VM clones to a different host, including troubleshooting information, see Chapter 9, Migrating virtual machines.

Chapter 9. Migrating virtual machines

If the current host of a virtual machine (VM) becomes unsuitable or cannot be used anymore, or if you want to redistribute the hosting workload, you can migrate the VM to another KVM host.

9.1. How migrating virtual machines works

The essential part of virtual machine (VM) migration is copying the XML configuration of a VM to a different host machine. If the migrated VM is not shut down, the migration also transfers the state of the VM’s memory and any virtualized devices to a destination host machine. For the VM to remain functional on the destination host, the VM’s disk images must remain available to it.

By default, the migrated VM is transient on the destination host, and remains defined also on the source host.

You can migrate a running VM using live or non-live migrations. To migrate a shut-off VM, you must use an offline migration. For details, see the following table.

Table 9.1. VM migration types

Migration typeDescriptionUse caseStorage requirements

Live migration

The VM continues to run on the source host machine while KVM is transferring the VM’s memory pages to the destination host. When the migration is nearly complete, KVM very briefly suspends the VM, and resumes it on the destination host.

Useful for VMs that require constant uptime. However, VMs that modify memory pages faster than KVM can transfer them, such as VMs under heavy I/O load, cannot be live-migrated, and non-live migration must be used instead.

The VM’s disk images must be located on a shared network, accessible both to the source host and the destination host.

Non-live migration

Suspends the VM, copies its configuration and its memory to the destination host, and resumes the VM.

Creates downtime for the VM, but is generally more reliable than live migration. Recommended for VMs under heavy I/O load.

The VM’s disk images must be located on a shared network, accessible both to the source host and the destination host.

Offline migration

Moves the VM’s configuration to the destination host

Recommended for shut-off VMs.

The VM’s disk images do not have to be available on a shared network, and can be copied or moved manually to the destination host instead.

Additional resources

9.2. Benefits of migrating virtual machines

Migrating virtual machines (VMs) can be useful for:

Load balancing
VMs can be moved to host machines with lower usage if their host becomes overloaded, or if another host is under-utilized.
Hardware independence
When you need to upgrade, add, or remove hardware devices on the host machine, you can safely relocate VMs to other hosts. This means that VMs do not experience any downtime for hardware improvements.
Energy saving
VMs can be redistributed to other hosts, and the unloaded host systems can thus be powered off to save energy and cut costs during low usage periods.
Geographic migration
VMs can be moved to another physical location for lower latency or when required for other reasons.

9.3. Limitations for migrating virtual machines

Before migrating virtual machines (VMs) in RHEL 8, ensure you are aware of the migration’s limitations.

  • Live storage migration cannot be performed on RHEL 8, but you can migrate storage while the VM is powered down. Note that live storage migration is available on Red Hat Virtualization.
  • Migrating VMs from or to a user session of libvirt is unreliable and therefore not recommended.

  • VMs that use certain features and configurations will not work correctly if migrated, or the migration will fail. Such features include:

    • Device passthrough
    • SR-IOV device assignment
    • Mediated devices, such as vGPUs
    • Non-Uniform Memory Access (NUMA) pinning

9.4. Sharing virtual machine disk images with other hosts

To perform a live migration of a virtual machine (VM) between supported KVM hosts, shared VM storage is required. This section provides instructions for sharing a locally stored VM image with the source host and the destination host using the NFS protocol.

Prerequisites

  • The VM intended for migration is shut down.
  • Optional: A host system is available for hosting the storage that is not the source or destination host, but both the source and the destination host can reach it through the network. This is the optimal solution for shared storage and is recommended by Red Hat.
  • Make sure that NFS file locking is not used as it is not supported in KVM.

  • The NFS is installed and enabled on the source and destination hosts. If it is not:

    1. Install the NFS packages: 

      # yum install nfs-utils

    2. Make sure that the ports for NFS in iptables (such as 2049) are open in the firewall. 

      # firewall-cmd --permanent --add-service=nfs
# firewall-cmd --permanent --add-service=mountd
# firewall-cmd --permanent --add-service=rpc-bind
# firewall-cmd --permanent --add-port=2049/tcp
# firewall-cmd --permanent --add-port=2049/udp
# firewall-cmd --reload

    3. Start the NFS service. 

      # systemctl start nfs-server

Procedure

  1. Connect to the host that will provide shared storage. In this example, it is the cargo-bay host: 

    # ssh root@cargo-bay
root@cargo-bay's password:
Last login: Mon Sep 24 12:05:36 2019
root~#

  2. Create a directory that will hold the disk image and will be shared with the migration hosts. 

    # mkdir /var/lib/libvirt/shared-images

  3. Copy the disk image of the VM from the source host to the newly created directory. For example, the following copies the disk image of the wanderer1 VM to the /var/lib/libvirt/shared-images/ directory on the`cargo-bay` host: 

    # scp /var/lib/libvirt/images/wanderer1.qcow2 root@cargo-bay:/var/lib/libvirt/shared-images/wanderer1.qcow2

  4. On the host that you want to use for sharing the storage, add the sharing directory to the /etc/exports file. The following example shares the /var/lib/libvirt/shared-images directory with the source-example and dest-example hosts: 

    /var/lib/libvirt/shared-images source-example(rw,no_root_squash) dest-example(rw,no_root_squash)

  5. On both the source and destination host, mount the shared directory in the /var/lib/libvirt/images directory: 

    # mount cargo-bay:/var/lib/libvirt/shared-images /var/lib/libvirt/images

Verification

  • To verify the process was successful, start the VM on the source host and observe if it boots correctly.

Additional resources

  • For detailed information on configuring NFS, opening IP tables, and configuring the firewall, see Exporting NFS shares.

9.5. Migrating a virtual machine using the command-line interface

If the current host of a virtual machine (VM) becomes unsuitable or cannot be used anymore, or if you want to redistribute the hosting workload, you can migrate the VM to another KVM host. This section provides instructions and examples for various scenarios of such migrations.

Prerequisites

  • The source host and the destination host both use the KVM hypervisor.
  • The source host and the destination host are able to reach each other over the network. Use the ping utility to verify this.
  • For the migration to be supportable by Red Hat, the source host and destination host must be using specific operating systems and machine types. To ensure this is the case, see the VM migration compatibility table.

  • Red Hat recommends for the disk images of VMs that will be migrated to be located on a separate networked location accessible to both the source host and the destination host. This is optional for offline migration, but required for migrating a running VM.

    For instructions to set up such shared VM storage, see Section 9.4, “Sharing virtual machine disk images with other hosts”.

  • When migrating an existing VM in a public bridge tap network, the source and destination hosts must be located on the same network. Otherwise, the VM network will not operate after migration.

Procedure

  1. Ensure that the libvirtd service is enabled and running. 

    # systemctl enable libvirtd.service
# systemctl restart libvirtd.service

  2. Use the virsh migrate command with options appropriate for your migration requirements.

    • The following migrates the wanderer1 VM from your local host to the system session of the dest-example host. The VM will remain running during the migration. 

      # virsh migrate --persistent --live wanderer1 qemu+ssh://dest-example/system

    • The following enables you to make manual adjustments to the configuration of the wanderer2 VM running on your local host, and then migrates the VM to the dest-example host. The migrated VM will automatically use the updated configuration. 

      # virsh dumpxml --migratable wanderer2 >wanderer2.xml
# vi wanderer2.xml
# virsh migrate --live --persistent --xml wanderer2.xml wanderer2 qemu+ssh://dest-example/system

      This procedure can be useful for example when the destination host needs to use a different path to access the shared VM storage or when configuring a feature specific to the destination host.

    • The following suspends the wanderer3 VM from the source-example host, migrates it to the dest-example host, and instructs it to use the adjusted XML configuration, provided by the wanderer3-alt.xml file. When the migration is completed, libvirt resumes the VM on the destination host. 

      # virsh migrate wanderer3 qemu+ssh://source-example/system qemu+ssh://dest-example/system --xml wanderer3-alt.xml

      After the migration, the VM remains in the suspended state on the source host, and the migrated copy is deleted after it is shut down.

    • The following deletes the shut-down wanderer4 VM from the source-example host, and moves its configuration to the dest-example host. 

      # virsh migrate --offline --persistent --undefinesource wanderer4 qemu+ssh://source-example/system qemu+ssh://dest-example/system

      Note that this type of migration does not require moving the VM’s disk image to shared storage. However, for the VM to be usable on the destination host, you need to migrate the VM’s disk image. For example: 

      # scp root@source-example:/var/lib/libvirt/images/wanderer4.qcow2 root@dest-example:/var/lib/libvirt/images/wanderer4.qcow2

  3. Wait for the migration to complete. The process may take some time depending on network bandwidth, system load, and the size of the VM. If the --verbose option is not used for virsh migrate, the CLI does not display any progress indicators except errors.

    When the migration is in progress, you can use the virsh domjobinfo utility to display the migration statistics.

Verification

  • On the destination host, list the available VMs to verify if the VM has been migrated: 

    # virsh list
Id Name                 State
----------------------------------
10 wanderer1              running

    Note that if the migration is still running, this command will list the VM state as paused.

Troubleshooting

  • In some cases, the target host will not be compatible with certain values of the migrated VM’s XML configuration, such as the network name or CPU type. As a result, the VM will fail to boot on the target host. To fix these problems, you can update the problematic values by using the virsh edit command.

  • If a live migration is taking a long time to complete, this may be because the VM is under heavy load and too many memory pages are changing for live migration to be possible. To fix this problem, change the migration to a non-live one by suspending the VM. 

    # virsh suspend wanderer1

Additional resources

  • For further options and examples for virtual machine migration, use virsh migrate --help or see the virsh man page.

9.6. Supported hosts for virtual machine migration

For the virtual machine (VM) migration to work properly and be supported by Red Hat, the source and destination hosts must be specific RHEL versions and machine types. The following table shows supported VM migration paths.

Table 9.2. Live migration compatibility

Migration methodRelease typeExampleSupport status

Forward

Major release

7.6+ → 8.1

On supported RHEL 7 systems: machine types i440fx and q35

Backward

Major release

8.1 → 7.6+

On supported RHEL 8 systems: machine types i440fx and q35

Forward

Minor release

8.0.1+ → 8.1+

On supported RHEL 7 systems: machine types i440fx and q35 on RHEL 7.6.0 and later.

On supported RHEL 8 systems: machine type q35.

Backward

Minor release

8.1 → 8.0.1

On supported RHEL 7 systems. Fully supported for machine types i440fx and q35.

On supported RHEL 8 systems: machine type q35.

Additional resources

9.7. Additional resources

  • You can also migrate VMs from a non-KVM hypervisor to a RHEL 7 or RHEL 8 host. This is also referred to as a V2V conversion, and you can find additional information and instructions in the Red Hat Knowledgebase.

Chapter 10. Managing virtual devices

One of the most effective ways to manage the functionality, features, and performance of a virtual machine (VM) is to adjust its virtual devices.

The following sections provide a general overview of what virtual devices are, and instructions on how they can be attached, modified, or removed from a VM.

10.1. How virtual devices work

The basics

Just like physical machines, virtual machines (VMs) require specialized devices to provide functions to the system, such as processing power, memory, storage, networking, or graphics. Physical systems usually use hardware devices for these purposes. However, because VMs work as software implements, they need to use software abstractions of such devices instead, referred to as virtual devices.

Virtual devices attached to a VM can be configured when creating the VM, and can also be managed on an existing VM. Generally, virtual devices can be attached or detached from a VM only when the VM is shut off, but some can be added or removed when the VM is running. This feature is referred to as device hot plug and hot unplug.

When creating a new VM, libvirt automatically creates and configures a default set of essential virtual devices, unless specified otherwise by the user. These are based on the host system architecture and machine type, and usually include:

  • the CPU
  • memory
  • a keyboard
  • a network interface controller (NIC)
  • various device controllers
  • a video card
  • a sound card

To manage virtual devices after the VM is created, use the command-line interface (CLI). However, to manage virtual storage devices and NICs, you can also use the RHEL 8 web console.

Performance or flexibility

For some types of devices, RHEL 8 supports multiple implementations, often with a trade-off between performance and flexibility.

For example, the physical storage used for virtual disks can be represented by files in various formats, such as qcow2 or raw, and presented to the VM using a variety of controllers:

  • an emulated controller
  • virtio-scsi
  • virtio-blk

An emulated controller is slower than a virtio controller, because virtio devices are designed specifically for virtualization purposes. On the other hand, emulated controllers make it possible to run operating systems that have no drivers for virtio devices. Similarly, virtio-scsi offers a more complete support for SCSI commands, and makes it possible to attach a larger number of disks to the VM. Finally, virtio-blk provides better performance than both virtio-scsi and emulated controllers, but a more limited range of use-cases. For example, attaching a physical disk as a LUN device to a VM is not possible when using virtio-blk.

For more information on types of virtual devices, see Section 10.5, “Types of virtual devices”.

Additional resources

10.2. Attaching devices to virtual machines

The following provides general information about creating and attaching virtual devices to your virtual machines (VMs) using the command-line interface (CLI). Some devices can also be attached to VMs using the RHEL 8 web console.

Prerequisites

  • Obtain the required options for the device you intend to attach to a VM. To see the available options for a specific device, use the virt-xml --device=? command. For example: 

    # virt-xml --network=?
--network options:
[...]
address.unit
boot_order
clearxml
driver_name
[...]

Procedure

  1. To attach a device to a VM, use the virt-xml --add-device command, including the definition of the device and the required options:

    • For example, the following command creates a 20GB newdisk qcow2 disk image in the /var/lib/libvirt/images/ directory, and attaches it as a virtual disk to the running testguest VM on the next start-up of the VM: 

      # virt-xml testguest --add-device --disk /var/lib/libvirt/images/newdisk.qcow2,format=qcow2,size=20
Domain 'testguest' defined successfully.
Changes will take effect after the domain is fully powered off.

    • The following attaches a USB flash drive, attached as device 004 on bus 002 on the host, to the testguest2 VM while the VM is running: 

      # virt-xml testguest2 --add-device --update --hostdev 002.004
Device hotplug successful.
Domain 'testguest2' defined successfully.

      The bus-device combination for defining the USB can be obtained using the lsusb command.

Verification

To verify the device has been added, do any of the following:

  • Use the virsh dumpxml command and see if the device’s XML definition has been added to the <devices> section in the VM’s XML configuration.

    For example, the following output shows the configuration of the testguest VM and confirms that the 002.004 USB flash disk device has been added. 

    # virsh dumpxml testguest
[...]
<hostdev mode='subsystem' type='usb' managed='yes'>
  <source>
    <vendor id='0x4146'/>
    <product id='0x902e'/>
    <address bus='2' device='4'/>
  </source>
  <alias name='hostdev0'/>
  <address type='usb' bus='0' port='3'/>
</hostdev>
[...]
  • Run the VM and test if the device is present and works properly.

Additional resources

  • For further information on using the virt-xml command, use man virt-xml.

10.3. Modifying devices attached to virtual machines

The following procedure provides general instructions for modifying virtual devices using the command-line interface (CLI). Some devices attached to your VM, such as disks and NICs, can also be modified using the RHEL 8 web console.

Prerequisites

  • Obtain the required options for the device you intend to attach to a VM. To see the available options for a specific device, use the virt-xml --device=? command. For example: 
# virt-xml --network=?
--network options:
[...]
address.unit
boot_order
clearxml
driver_name
[...]
  • Optional: Back up the XML configuration of your VM by using virsh dumpxml vm-name and sending the output to a file. For example, the following backs up the configuration of your Motoko VM as the motoko.xml file: 
# virsh dumpxml Motoko > motoko.xml
# cat motoko.xml
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>Motoko</name>
  <uuid>ede29304-fe0c-4ca4-abcd-d246481acd18</uuid>
  [...]
</domain>

Procedure

  1. Use the virt-xml --edit command, including the definition of the device and the required options:

    For example, the following clears the <cpu> configuration of the shut-off testguest VM and sets it to host-model: 

    # virt-xml testguest --edit --cpu host-model,clearxml=yes
Domain 'testguest' defined successfully.

Verification

To verify the device has been modified, do any of the following:

  • Run the VM and test if the device is present and reflects the modifications.

  • Use the virsh dumpxml command and see if the device’s XML definition has been modified in the VM’s XML configuration.

    For example, the following output shows the configuration of the testguest VM and confirms that the CPU mode has been configured as host-model. 

    # virsh dumpxml testguest
[...]
<cpu mode='host-model' check='partial'>
  <model fallback='allow'/>
</cpu>
[...]

Troubleshooting

  • If modifying a device causes your VM to become unbootable, use the virsh define utility to restore the XML configuration by reloading the XML configuration file you backed up previously. 

    # virsh define testguest.xml
Note

For small changes to the XML configuration of your VM, you can use the virsh edit command - for example virsh edit testguest. However, do not use this method for more extensive changes, as it is more likely to break the configuration in ways that could prevent the VM from booting.

Additional resources

  • For details on using the virt-xml command, use man virt-xml.

10.4. Removing devices from virtual machines

The following provides general information for removing virtual devices from your virtual machines (VMs) using the command-line interface (CLI). Some devices, such as disks or NICs, can also be removed from VMs using the RHEL 8 web console.

Prerequisites

  • Optional: Back up the XML configuration of your VM by using virsh dumpxml vm-name and sending the output to a file. For example, the following backs up the configuration of your Motoko VM as the motoko.xml file: 
# virsh dumpxml Motoko > motoko.xml
# cat motoko.xml
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>Motoko</name>
  <uuid>ede29304-fe0c-4ca4-abcd-d246481acd18</uuid>
  [...]
</domain>

Procedure

  1. Use the virt-xml --remove-device command, including a definition of the device. For example:

    • The following removes the storage device marked as vdb from the running testguest VM after it shuts down: 

      # virt-xml testguest --remove-device --disk target=vdb
Domain 'testguest' defined successfully.
Changes will take effect after the domain is fully powered off.

    • The following immediately removes a USB flash drive device from the running testguest2 VM: 

      # virt-xml testguest2 --remove-device --update --hostdev type=usb
Device hotunplug successful.
Domain 'testguest2' defined successfully.

Troubleshooting

  • If removing a device causes your VM to become unbootable, use the virsh define utility to restore the XML configuration by reloading the XML configuration file you backed up previously. 

    # virsh define testguest.xml

Additional resources

  • For details on using the virt-xml command, use man virt-xml.

10.5. Types of virtual devices

Virtualization in RHEL 8 can present several distinct types of virtual devices that you can attach to virtual machines (VMs):

Emulated devices

Emulated devices are software implementations of widely used physical devices. Drivers designed for physical devices are also compatible with emulated devices. Therefore, emulated devices can be used very flexibly.

However, since they need to faithfully emulate a particular type of hardware, emulated devices may suffer a significant performance loss compared with the corresponding physical devices or more optimized virtual devices.

The following types of emulated devices are supported:

  • Virtual CPUs (vCPUs), with a large choice of CPU models available. The performance impact of emulation depends significantly on the differences between the host CPU and the emulated vCPU.
  • Emulated system components, such as PCI bus controllers
  • Emulated storage controllers, such as SATA, SCSI or even IDE
  • Emulated sound devices, such as ICH9, ICH6 or AC97
  • Emulated graphics cards, such as VGA or QXL cards
  • Emulated network devices, such as rtl8139
Paravirtualized devices

Paravirtualization provides a fast and efficient method for exposing virtual devices to VMs. Paravirtualized devices expose interfaces that are designed specifically for use in VMs, and thus significantly increase device performance. RHEL 8 provides paravirtualized devices to VMs using the virtio API as a layer between the hypervisor and the VM. The drawback of this approach is that it requires a specific device driver in the guest operating system.

It is recommended to use paravirtualized devices instead of emulated devices for VM whenever possible, notably if they are running I/O intensive applications. Paravirtualized devices decrease I/O latency and increase I/O throughput, in some cases bringing them very close to bare-metal performance. Other paravirtualized devices also add functionality to VMs that is not otherwise available.

The following types of paravirtualized devices are supported:

  • The paravirtualized network device (virtio-net).

  • Paravirtualized storage controllers:

    • virtio-blk - provides block device emulation.
    • virtio-scsi - provides more complete SCSI emulation.
  • The paravirtualized clock.
  • The paravirtualized serial device (virtio-serial).

  • The balloon device (virtio-balloon), used to share information about guest memory usage with the hypervisor.

    Note, however, that the balloon device also requires the balloon service to be installed.

  • The paravirtualized random number generator (virtio-rng).
  • The paravirtualized graphics card (QXL).
Physically shared devices

Certain hardware platforms enable VMs to directly access various hardware devices and components. This process is known as device assignment or passthrough.

When attached in this way, some aspects of the physical device are directly available to the VM as they would be to a physical machine. This provides superior performance for the device when used in the VM. However, devices physically attached to a VM become unavailable to the host, and also cannot be migrated.

Nevertheless, some devices can be shared across multiple VMs. For example, a single physical device can in certain cases provide multiple mediated devices, which can then be assigned to distinct VMs.

The following types of passthrough devices are supported:

  • Virtual Function I/O (VFIO) device assignment - safely exposes devices to applications or VMs using hardware-enforced DMA and interrupt isolation.
  • USB, PCI, and SCSI passthrough - expose common industry standard buses directly to VMs in order to make their specific features available to guest software.
  • Single-root I/O virtualization (SR-IOV) - a specification that enables hardware-enforced isolation of PCI Express resources. This makes it safe and efficient to partition a single physical PCI resource into virtual PCI functions. It is commonly used for network interface cards (NICs).
  • N_Port ID virtualization (NPIV) - a Fibre Channel technology to share a single physical host bus adapter (HBA) with multiple virtual ports.
  • GPUs and vGPUs - accelerators for specific kinds of graphic or compute workloads. Some GPUs can be attached directly to a VM, while certain types also offer the ability to create virtual GPUs (vGPUs) that share the underlying physical hardware.

10.6. Managing virtual USB devices

When using a virtual machine (VM), you can access and control a USB device, such as a flash drive or a web camera, that is attached to the host system. In this scenario, the host system passes control of the device to the VM. This is also known as a USB-passthrough.

The following sections provide information about using the command line to:

10.6.1. Attaching USB devices to virtual machines

To attach a USB device to a virtual machine (VM), you can include the USB device information in the XML configuration file of the VM.

Prerequisites

  • Ensure the device you want to pass through to the VM is attached to the host.

Procedure

  1. Locate the bus and device values of the USB that you want to attach to the VM.

    For example, the following command displays a list of USB devices attached to the host. The device we will use in this example is attached on bus 001 as device 005. 

    # lsusb
[...]
Bus 001 Device 003: ID 2567:0a2b Intel Corp.
Bus 001 Device 005: ID 0407:6252 Kingston River 2.0
[...]

  2. Use the virt-xml utility along with the --add-device argument.

    For example, the following command attaches a USB flash drive to the Library VM. 

    # virt-xml Library --add-device --hostdev 001.005
Domain 'Library' defined successfully.
Note

To attach a USB device to a running VM, add the --update argument to the previous command.

Verification steps

  • Run the VM and test if the device is present and works as expected.

  • Use the virsh dumpxml command to see if the device’s XML definition has been added to the <devices> section in the VM’s XML configuration file. 

    # virsh dumpxml Library
[...]
<hostdev mode='subsystem' type='usb' managed='yes'>
  <source>
    <vendor id='0x0407'/>
    <product id='0x6252'/>
    <address bus='1' device='5'/>
  </source>
  <alias name='hostdev0'/>
  <address type='usb' bus='0' port='3'/>
</hostdev>
[...]

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.6.2. Removing USB devices from virtual machines

To remove a USB device from a virtual machine (VM), you can remove the USB device information from the XML configuration of the VM.

Procedure

  1. Locate the bus and device values of the USB that you want to remove from the VM.

    For example, the following command displays a list of USB devices attached to the host. The device we will use in this example is attached on bus 001 as device 005. 

    # lsusb
[...]
Bus 001 Device 003: ID 2567:0a2b Intel Corp.
Bus 001 Device 005: ID 0407:6252 Kingston River 2.0
[...]

  2. Use the virt-xml utility along with the --remove-device argument.

    For example, the following command removes a USB flash drive, attached to the host as device 005 on bus 001, from the Library VM. 

    # virt-xml Library --remove-device --hostdev 001.005
Domain 'Library' defined successfully.
Note

To remove a USB device from a running VM, add the --update argument to the previous command.

Verification steps

  • Run the VM and check if the device has been removed from the list of devices.

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.6.3. Additional resources

10.7. Managing virtual optical drives

When using a virtual machine (VM), you can access information stored in an ISO image on the host. To do so, attach the ISO image to the VM as a virtual optical drive, such as a CD drive or a DVD drive.

The following sections provide information about using the command line to:

10.7.1. Attaching optical drives to virtual machines

To attach an ISO image as a virtual optical drive, edit the XML configuration file of the virtual machine (VM) and add the new drive.

Prerequisites

  • You must store the ISO image on the local host.
  • You must know the path to the ISO image.

Procedure

  • Use the virt-xml utility with the --add-device argument.

    For example, the following command attaches the Doc10 ISO image, stored in the /MC/tank/ directory, to the DN1 VM. 

    # virt-xml DN1 --add-device --disk /MC/tank/Doc10.iso,device=cdrom
Domain 'DN1' defined successfully.

Verification steps

  • Run the VM and test if the device is present and works as expected.

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.7.2. Replacing ISO images in virtual optical drives

To replace an ISO image attached as a virtual optical drive to a virtual machine (VM), edit the XML configuration file of the VM and specify the replacement.

Prerequisites

  • You must store the ISO image on the local host.
  • You must know the path to the ISO image.

Procedure

  1. Locate the target device where the CD-ROM is attached to the VM. You can find this information in the VM’s XML configuration file.

    For example, the following command displays the DN1 VM’s XML configuration file, where the target device for CD-ROM is sda. 

    # virsh dumpxml DN1
...
<disk>
  ...
  <source file='/MC/tank/Doc10.iso'/>
  <target dev='sda' bus='sata'/>
  ...
</disk>
...

  2. Use the virt-xml utility with the --edit argument.

    For example, the following command replaces the Doc10 ISO image, attached to the DN1 VM at target sda, with the DrDN ISO image stored in the /Dvrs/current/ directory. 

    # virt-xml DN1 --edit target=sda --disk /Dvrs/current/DrDN.iso
Domain 'DN1' defined successfully.

Verification steps

  • Run the VM and test if the device is replaced and works as expected.

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.7.3. Removing ISO images from virtual optical drives

To remove an ISO image from a virtual optical drive attached to a virtual machine (VM), edit the XML configuration file of the VM.

Procedure

  1. Locate the target device where the CD-ROM is attached to the VM. You can find this information in the VM’s XML configuration file.

    For example, the following command displays the DN1 VM’s XML configuration file, where the target device for CD-ROM is sda. 

    # virsh dumpxml DN1
...
<disk>
  ...
  <source file='/Dvrs/current/DrDN'/>
  <target dev='sda' bus='sata'/>
  ...
</disk>
...

  2. Use the virt-xml utility with the --edit argument.

    For example, the following command removes the DrDN ISO image from the CD drive attached to the DN1 VM. 

    # virt-xml DN1 --edit target=sda --disk path=
Domain 'DN1' defined successfully.

Verification steps

  • Run the VM and check that image is no longer available.

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.7.4. Removing optical drives from virtual machines

To remove an optical drive attached to a virtual machine (VM), edit the XML configuration file of the VM.

Procedure

  1. Locate the target device where the CD-ROM is attached to the VM. You can find this information in the VM’s XML configuration file.

    For example, the following command displays the DN1 VM’s XML configuration file, where the target device for CD-ROM is sda. 

    # virsh dumpxml DN1
...
<disk type='file' device='cdrom'>
  <driver name='qemu' type='raw'/>
  <target dev='sda' bus='sata'/>
  ...
</disk>
...

  2. Use the virt-xml utility with the --remove-device argument.

    For example, the following command removes the optical drive attached as target sda from the DN1 VM. 

    # virt-xml DN1 --remove-device --disk target=sda
Domain 'DN1' defined successfully.

Verification steps

  • Confirm that the device is no longer listed in the XML configuration file of the VM.

Additional resources

  • For other arguments, see the virt-xml(1) man page.

10.7.5. Additional resources

10.8. Managing SR-IOV devices

An emulated virtual device often uses more CPU and memory than a hardware network device. This can limit the performance of a virtual machine (VM). However, if any devices on your virtualization host support Single Root I/O Virtualization (SR-IOV), you can use this feature to improve the device performance, and possibly also the overall performance of your VMs.

10.8.1. What is SR-IOV?

Single-root I/O virtualization (SR-IOV) is a specification that enables a single PCI Express (PCIe) device to present multiple separate PCI devices, called virtual functions (VFs), to the host system. Each of these devices:

  • Is able to provide the same or similar service as the original PCIe device.
  • Appears at a different address on the host PCI bus.
  • Can be assigned to a different VM using VFIO assignment.

For example, a single SR-IOV capable network device can present VFs to multiple VMs. While all of the VFs use the same physical card, the same network connection, and the same network cable, each of the VMs directly controls its own hardware network device, and uses no extra resources from the host.

How SR-IOV works

The SR-IOV functionality is possible thanks to the introduction of the following PCIe functions:

  • Physical functions (PFs) - A PCIe function that provides the functionality of its device (for example networking) to the host, but can also create and manage a set of VFs. Each SR-IOV capable device has one or more PFs.
  • Virtual functions (VFs) - Lightweight PCIe functions that behave as independent devices. Each VF is derived from a PF. The maximum number of VFs a device can have depends on the device hardware. Each VF can be assigned only to a single VM at a time, but a VM can have multiple VFs assigned to it.

VMs recognize VFs as virtual devices. For example, a VF created by an SR-IOV network device appears as a network card to a VM to which it is assigned, in the same way as a physical network card appears to the host system.

Figure 10.1. SR-IOV architecture

virt SR IOV

Benefits

The primary advantages of using SR-IOV VFs rather than emulated devices are:

  • Improved performance
  • Reduced use of host CPU and memory resources

For example, a VF attached to a VM as a vNIC performs at almost the same level as a physical NIC, and much better than paravirtualized or emulated NICs. In particular, when multiple VFs are used simultaneously on a single host, the performance benefits can be significant.

Disadvantages

  • To modify the configuration of a PF, you must first change the number of VFs exposed by the PF to zero. Therefore, you also need to remove the devices provided by these VFs from the VM to which they are assigned.
  • A VM with an VFIO-assigned devices attached, including SR-IOV VFs, cannot be migrated to another host. In some cases, you can work around this limitation by pairing the assigned device with an emulated device. For example, you can bond an assigned networking VF to an emulated vNIC, and remove the VF before the migration.
  • In addition, VFIO-assigned devices require pinning of VM memory, which increases the memory consumption of the VM and prevents the use of memory ballooning on the VM.

Additional resources

10.8.2. Attaching SR-IOV networking devices to virtual machines

To attach an SR-IOV networking device to a virtual machine (VM) on an Intel or AMD host, you must create a virtual function (VF) from an SR-IOV capable network interface on the host and assign the VF as a device to a specified VM. For details, see the following instructions.

Prerequisites

  • The CPU and the firmware of your host support the I/O Memory Management Unit (IOMMU).

    • If using an Intel CPU, it must support the Intel Virtualization Technology for Directed I/O (VT-d).
    • If using an AMD CPU, it must support the AMD-Vi feature.

  • The host system uses Access Control Service (ACS) to provide direct memory access (DMA) isolation for PCIe topology. Verify this with the system vendor.

    For additional information, see Hardware Considerations for Implementing SR-IOV.

  • The physical network device supports SR-IOV. To verify if any network devices on your system support SR-IOV, use the lspci -v command and look for Single Root I/O Virtualization (SR-IOV) in the output. 

    # lspci -v
[...]
02:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
	Subsystem: Intel Corporation Gigabit ET Dual Port Server Adapter
	Flags: bus master, fast devsel, latency 0, IRQ 16, NUMA node 0
	Memory at fcba0000 (32-bit, non-prefetchable) [size=128K]
[...]
	Capabilities: [150] Alternative Routing-ID Interpretation (ARI)
	Capabilities: [160] Single Root I/O Virtualization (SR-IOV)
	Kernel driver in use: igb
	Kernel modules: igb
[...]

  • The host network interface you want to use for creating VFs is running. For example, to activate the eth1 interface and verify it is running: 

    # ip link set eth1 up
# ip link show eth1
8: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT qlen 1000
   link/ether a0:36:9f:8f:3f:b8 brd ff:ff:ff:ff:ff:ff
   vf 0 MAC 00:00:00:00:00:00, spoof checking on, link-state auto
   vf 1 MAC 00:00:00:00:00:00, spoof checking on, link-state auto
   vf 2 MAC 00:00:00:00:00:00, spoof checking on, link-state auto
   vf 3 MAC 00:00:00:00:00:00, spoof checking on, link-state auto

  • For SR-IOV device assignment to work, the IOMMU feature must be enabled in the host BIOS and kernel. To do so:

    • On an Intel host, enable VT-d:

      • If your Intel host uses multiple boot entries:

        1. Edit the /etc/default/grub file and add the intel_iommu=on and iommu=pt parameters at the end of the GRUB_CMDLINE_LINUX line: 

          GRUB_CMDLINE_LINUX="crashkernel=auto resume=/dev/mapper/rhel_dell-per730-27-swap rd.lvm.lv=rhel_dell-per730-27/root rd.lvm.lv=rhel_dell-per730-27/swap console=ttyS0,115200n81 intel_iommu=on iommu=pt"

        2. Regenerate the GRUB configuration: 

          # grub2-mkconfig -o /boot/grub2/grub.cfg
        3. Reboot the host.

      • If your Intel host uses a single boot entry:

        1. Regenerate the GRUB configuration with the intel_iommu=on parameter: 

          # grubby --args="intel_iommu=on" --update-kernel DEFAULT
        2. Reboot the host.

    • On an AMD host, enable AMD-Vi:

      • If your AMD host uses multiple boot entries:

        1. Edit the /etc/default/grub file and add the iommu=pt and amd_iommu=on parameters at the end of the GRUB_CMDLINE_LINUX line: 

          GRUB_CMDLINE_LINUX="crashkernel=auto resume=/dev/mapper/rhel_dell-per730-27-swap rd.lvm.lv=rhel_dell-per730-27/root rd.lvm.lv=rhel_dell-per730-27/swap console=ttyS0,115200n81 iommu=pt amd_iommu=on"

        2. Regenerate the GRUB configuration: 

          # grub2-mkconfig -o /boot/grub2/grub.cfg
        3. Reboot the host.

      • If your AMD host uses a single boot entry:

        1. Regenerate the GRUB configuration with the iommu=pt parameter: 

          # grubby --args="iommu=pt" --update-kernel DEFAULT
        2. Reboot the host.

Procedure

  1. Optional: Confirm the maximum number of VFs your network device can use. To do so, use the following command and replace eth1 with your SR-IOV compatible network device. 

    # cat /sys/class/net/eth1/device/sriov_totalvfs
7

  2. Use the following command to create a virtual function (VF): 

    # echo VF-number > /sys/class/net/network-interface/device/sriov_numvfs

    In the command, replace:

    • VF-number with the number of VFs you want to create on the PF.
    • network-interface with the name of the network interface for which the VFs will be created.

    The following example creates 2 VFs from the eth1 network interface: 

    # echo 2 > /sys/class/net/eth1/device/sriov_numvfs

  3. Verify the VFs have been added: 

    # lspci | grep Ethernet
01:00.0 Ethernet controller: Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
01:00.1 Ethernet controller: Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
07:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
07:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)

  4. Make the created VFs persistent by creating a udev rule for the network interface you used to create the VFs. For example, for the eth1 interface, create the /etc/udev/rules.d/eth1.rules file, and add the following line: 

    ACTION=="add", SUBSYSTEM=="net", ENV{ID_NET_DRIVER}=="ixgbe", ATTR{device/sriov_numvfs}="2"

    This ensures that the two VFs that use the ixgbe driver will automatically be available for the eth1 interface when the host starts.

    Warning

    Currently, this command does not work correctly when attempting to make VFs persistent on Broadcom NetXtreme II BCM57810 adapters. In addition, attaching VFs based on these adapters to Windows VMs is currently not reliable.

  5. Use the virsh nodedev-list command to verify that libvirt recognizes the added VF devices. For example, the following shows that the 01:00.0 and 07:00.0 PFs from the previous example have been successfully converted into VFs: 

    # virsh nodedev-list | grep pci_
pci_0000_01_00_0
pci_0000_01_00_1
pci_0000_07_10_0
pci_0000_07_10_1
[...]

  6. Obtain the bus, slot, and function values of a PF and one of its corresponding VFs. For example, for pci_0000_01_00_0 and pci_0000_01_00_1: 

    # virsh nodedev-dumpxml pci_0000_01_00_0
<device>
  <name>pci_0000_01_00_0</name>
  <path>/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0</path>
  <parent>pci_0000_00_01_0</parent>
  <driver>
    <name>ixgbe</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>1</bus>
    <slot>0</slot>
    <function>0</function>
[...]
# virsh nodedev-dumpxml pci_0000_01_00_1
<device>
  <name>pci_0000_01_00_1</name>
  <path>/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1</path>
  <parent>pci_0000_00_01_0</parent>
  <driver>
    <name>vfio-pci</name>
  </driver>
  <capability type='pci'>
    <domain>0</domain>
    <bus>1</bus>
    <slot>0</slot>
    <function>1</function>
[...]

  7. Create a temporary XML file and add a configuration into using the bus, slot, and function values you obtained in the previous step. For example: 

    <interface type='hostdev' managed='yes'>
  <source>
    <address type='pci' domain='0x0000' bus='0x03' slot='0x10' function='0x2'/>
  </source>
</interface>

  8. Add the VF to a VM using the temporary XML file. For example, the following attaches a VF saved in the /tmp/holdmyfunction.xml to a running testguest1 VM and ensures it is available after the VM restarts: 

    # virsh attach-device testguest1 /tmp/holdmyfunction.xml --live --config
Device attached successfully.

    If this is successful, the guest operating system detects a new network interface card.

10.8.3. Supported devices for SR-IOV assignment

Not all devices can be used for SR-IOV. The following devices have been tested and verified as compatible with SR-IOV in RHEL 8.

Networking devices

  • Intel 82599ES 10 Gigabit Ethernet Controller - uses the ixgbe driver
  • Intel Ethernet Controller XL710 Series - uses the i40e driver
  • Mellanox ConnectX-5 Ethernet Adapter Cards - use the mlx5_core driver
  • Intel Ethernet Network Adapter XXV710 - uses the i40e driver
  • Intel 82576 Gigabit Ethernet Controller - uses the igb driver
  • Broadcom NetXtreme II BCM57810 - uses the bnx2x driver

10.9. Attaching DASD devices to virtual machines on IBM Z

Direct-access storage devices (DASDs) provide a number of specific storage features. Using the vfio-ccw feature, you can assign DASDs as mediated devices to your virtual machines (VMs) on IBM Z hosts. This for example makes it possible for the VM to access a z/OS dataset, or to share the assigned DASDs with a z/OS machine.

Prerequisites

  • Your host system is using the IBM Z hardware architecture and supports the FICON protocol.
  • The target VM is using a Linux guest operating system.

  • The necessary kernel modules have been loaded on the host. To verify, use: 

    # lsmod | grep vfio

    The output should contain the following modules:

    • vfio_ccw
    • vfio_mdev
    • vfio_iommu_type1
  • You have a spare DASD device for exclusive use by the VM.

Procedure

  1. Obtain the device identifier of the DASD device. The lsdasd utility displays this as Bus-ID. 

    # lsdasd
Bus-ID    Status    Name      Device  Type         BlkSz  Size      Blocks
================================================================================
0.0.002c  active    dasdh     94:0    ECKD         4096   21129MB   5409180

    In the following commands of this procedure, replace 0.0.002c with the detected device identifier of your device.

  2. Obtain the subchannel path of the DASD device. 

    # lscss | grep 0.0.002c
0.0.002c 0.0.24ac  3390/0c 3990/e9 yes  f0  f0  ff   01021112 00000000

    In this example, the subchannel path is detected as 0.0.24ac. In the following commands of this procedure, replace 0.0.24ac with the detected subchannel path of your device.

  3. Unbind the DASD device from its subchannel on the host. 

    # echo 0.0.002c > /sys/bus/ccw/devices/0.0.002c/driver/unbind

  4. Unbind the subchannel from the I/O subchannel driver. 

    # echo 0.0.24ac > /sys/bus/css/devices/0.0.24ac/driver/unbind

  5. Bind the subchannel to the vfio_ccw passthrough driver. 

    # echo 0.0.24ac > /sys/bus/css/drivers/vfio_ccw/bind

  6. Generate an UUID. 

    # uuidgen
30820a6f-b1a5-4503-91ca-0c10ba12345a

  7. Create the DASD mediated device using the generated UUID 

    # echo "30820a6f-b1a5-4503-91ca-0c10ba12345a" > /sys/bus/css/devices/0.0.24ac/mdev_supported_types/vfio_ccw-io/create

  8. Attach the mediated device to the VM. To do so, use the virsh edit utility to edit the XML configuration of the VM, add the following section to the XML, and replace the uuid value with the UUID you generated in the previous step. 

    <hostdev mode='subsystem' type='mdev' model='vfio-ccw'>
  <source>
    <address uuid="30820a6f-b1a5-4503-91ca-0c10ba12345a"/>
  </source>
</hostdev>

Verification

  1. Obtain the identifier that libvirt assigned to the mediated DASD device. To do so, display the XML configuration of the VM and look for a vfio-ccw device. 

    # virsh dumpxml vm-name

<domain>
[...]
    <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-ccw'>
      <source>
        <address uuid='10620d2f-ed4d-437b-8aff-beda461541f9'/>
      </source>
      <alias name='hostdev0'/>
      <address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0009'/>
    </hostdev>
[...]
</domain>

    In this example, the assigned identifier of the device is 0.0.0009.

  2. Log in to the guest operating system of the VM and confirm that the device is listed. For example: 

    # lscss | grep 0.0.0009
0.0.0009 0.0.0007  3390/0c 3990/e9      f0  f0  ff   12212231 00000000

  3. Set the device online. For example: 

    # chccwdev -e 0.0009
Setting device 0.0.0009 online
Done

Chapter 11. Managing storage for virtual machines

You can manage virtual machine storage using the CLI or the web console.

This documentation provides information on how to manage virtual machine storage using the virsh command.

11.1. Understanding virtual machine storage

The following sections provide information about storage for virtual machines (VMs), including information about storage pools, storage volumes, and how they are used to provide storage for VMs.

11.1.1. Virtual machine storage

The following provides information about how storage pools and storage volumes are used to create storage for virtual machines (VMs).

A storage pool is a quantity of storage managed by the host and set aside for use by VMs. Storage volumes can be created from space in the storage pools. Each storage volume can be assigned to a VM as a block device, such as a disk, on a guest bus.

Storage pools and volumes are managed using libvirt. With the libvirt remote protocol, you can manage all aspects of VM storage. These operations can be performed on a remote host. As a result, a management application that uses libvirt, such as the RHEL web console, can be used to perform all the required tasks for configuring the storage for a VM.

The libvirt API can be used to query the list of volumes in the storage pool or to get information regarding the capacity, allocation, and available storage in the storage pool. A storage volume in the storage pool may be queried to get information such as allocation and capacity, which may differ for sparse volumes.

For storage pools that support it, the libvirt API can be used to create, clone, resize, and delete storage volumes. The APIs can also be used to upload data to storage volumes, download data from storage volumes, or wipe data from storage volumes.

Once a storage pool is started, a storage volume can be assigned to a VM using the storage pool name and storage volume name instead of the host path to the volume in the XML configuration files of the VM.

11.1.2. Storage pools

A storage pool is a file, directory, or storage device, managed by libvirt to provide storage to virtual machines (VMs). Storage pools are divided into storage volumes that store VM images or are attached to VMs as additional storage. Multiple VMs can share the same storage pool, allowing for better allocation of storage resources.

Storage pools can be persistent or transient:

  • A persistent storage pool survives a system restart of the host machine.
  • A transient storage pool only exists until the host reboots.

The virsh pool-define command is used to create a persistent storage pool, and the virsh pool-create command is used to create a transient storage pool.

Storage pool storage types

Storage pools can be either local or network-based (shared):

  • Local storage pools

    Local storage pools are attached directly to the host server. They include local directories, directly attached disks, physical partitions, and Logical Volume Management (LVM) volume groups on local devices.

    Local storage pools are useful for development, testing, and small deployments that do not require migration or large numbers of VMs.

  • Networked (shared) storage pools

    Networked storage pools include storage devices shared over a network using standard protocols.

Storage pool usage example

To illustrate the available options for managing storage pools, the following describes a sample NFS server that uses mount -t nfs nfs.example.com:/path/to/share /path/to/data.

A storage administrator could define an NFS Storage Pool on the virtualization host to describe the exported server path and the client target path. This will allow libvirt to perform the mount either automatically when libvirt is started or as needed while libvirt is running. Files with the NFS Server exported directory are listed as storage volumes within the NFS storage pool.

When the storage volume is added to the VM, the administrator does not need to add the target path to the volume. They just needs to add the storage pool and storage volume by name. Therefore, if the target client path changes, it does not affect the VM.

When the storage pool is started, libvirt mounts the share on the specified directory, just as if the system administrator logged in and executed mount nfs.example.com:/path/to/share /vmdata. If the storage pool is configured to autostart, libvirt ensures that the NFS shared disk is mounted on the directory specified when libvirt is started.

Once the storage pool is started, the files in the NFS shared disk are reported as storage volumes, and the storage volumes' paths may be queried using the libvirt API. The storage volumes' paths can then be copied into the section of a VM’s XML definition that describes the source storage for the VM’s block devices. In the case of NFS, an application that uses the libvirt API can create and delete storage volumes in the storage pool (files in the NFS share) up to the limit of the size of the pool (the storage capacity of the share).

Stopping (destroying) a storage pool removes the abstraction of the data, but keeps the data intact.

Not all storage pool types support creating and deleting volumes. Stopping the storage pool (pool-destroy) undoes the start operation, in this case, unmounting the NFS share. The data on the share is not modified by the destroy operation, despite what the name of the command suggests. For more details, see man virsh.

Supported and unsupported storage pool types

The following is a list of storage pool types supported by RHEL:

  • Directory-based storage pools
  • Disk-based storage pools
  • Partition-based storage pools
  • GlusterFS storage pools
  • iSCSI-based storage pools
  • LVM-based storage pools
  • NFS-based storage pools
  • SCSI-based storage pools with vHBA devices
  • Multipath-based storage pools
  • RBD-based storage pools

The following is a list of libvirt storage pool types that are not supported by RHEL:

  • Sheepdog-based storage pools
  • Vstorage-based storage pools
  • ZFS-based storage pools

11.1.3. Storage volumes

Storage pools are divided into storage volumes. Storage volumes are abstractions of physical partitions, LVM logical volumes, file-based disk images, and other storage types handled by libvirt. Storage volumes are presented to VMs as local storage devices, such as disks, regardless of the underlying hardware.

On the host machine, a storage volume is referred to by its name and an identifier for the storage pool from which it derives. On the virsh command line, this takes the form --pool storage_pool volume_name.

For example, to display information about a volume named firstimage in the guest_images pool. 

# virsh vol-info --pool guest_images firstimage
  Name:             firstimage
  Type:             block
  Capacity:         20.00 GB
  Allocation:       20.00 GB

11.2. Managing storage for virtual machines using the CLI

The following documentation provides information on how to manage virtual machine (VM) storage using the virsh command-line utility.

Using virsh, you can add, remove, and modify VM storage, as well as view information about VM storage.

Note

In many cases, storage for a VM is created at the same time the VM is created. Therefore, the following information primarily relates to advanced management of VM storage.

11.2.1. Viewing virtual machine storage information using the CLI

The following provides information about viewing information about storage pools and storage volumes using the CLI.

11.2.1.1. Viewing storage pool information using the CLI

Using the CLI, you can view a list of all storage pools with limited or full details about the storage pools. You can also filter the storage pools listed.

Procedure

  • Use the virsh pool-list command to view storage pool information. 

    # virsh pool-list --all --details
 Name                State    Autostart  Persistent    Capacity  Allocation   Available
 default             running  yes        yes          48.97 GiB   23.93 GiB   25.03 GiB
 Downloads           running  yes        yes         175.62 GiB   62.02 GiB  113.60 GiB
 RHEL8-Storage-Pool  running  yes        yes         214.62 GiB   93.02 GiB  168.60 GiB

Additional resources

  • For information on the available virsh pool-list options, use the virsh pool-list --help command.

11.2.1.2. Viewing storage volume information using the CLI

The following provides information on viewing information about storage pools. You can view a list of all storage pools in a specified storage pool and details about a specified storage pool.

Procedure

  1. Use the virsh vol-list command to list the storage volumes in a specified storage pool. 

    # virsh vol-list --pool RHEL8-Storage-Pool --details
 Name                Path                                               Type   Capacity  Allocation
---------------------------------------------------------------------------------------------
 .bash_history       /home/VirtualMachines/.bash_history       file  18.70 KiB   20.00 KiB
 .bash_logout        /home/VirtualMachines/.bash_logout        file    18.00 B    4.00 KiB
 .bash_profile       /home/VirtualMachines/.bash_profile       file   193.00 B    4.00 KiB
 .bashrc             /home/VirtualMachines/.bashrc             file   1.29 KiB    4.00 KiB
 .git-prompt.sh      /home/VirtualMachines/.git-prompt.sh      file  15.84 KiB   16.00 KiB
 .gitconfig          /home/VirtualMachines/.gitconfig          file   167.00 B    4.00 KiB
 RHEL8_Volume.qcow2  /home/VirtualMachines/RHEL8_Volume.qcow2  file  60.00 GiB   13.93 GiB

  2. Use the virsh vol-info command to list the storage volumes in a specified storage pool. 

    # vol-info --pool RHEL8-Storage-Pool --vol RHEL8_Volume.qcow2
Name:           RHEL8_Volume.qcow2
Type:           file
Capacity:       60.00 GiB
Allocation:     13.93 GiB

11.2.2. Creating and assigning storage for virtual machines using the CLI

The following is a high-level procedure for creating and assigning storage for virtual machines (VMs):

  1. Create storage pools

    Create one or more storage pools from available storage media. For a list of supported storage pool types, see Storage pool types.

    • To create persistent storage pools, use the virsh pool-define-as and virsh pool-define commands.

      The virsh pool-define-as command places the options in the command line. The virsh pool-define command uses an XML file for the pool options.

    • To create temporary storage pools, use the virsh pool-create and virsh pool-create-as commands.

      The virsh pool-create-as command places the options in the command line. The virsh pool-create command uses an XML file for the pool options.

  1. Create storage volumes

    Create one or more storage volumes from the available storage pools.

  2. Assign storage devices to a VM

    Assign one or more storage devices abstracted from storage volumes to a VM.

The following sections provide information on creating and assigning storage using the CLI:

11.2.2.1. Creating and assigning directory-based storage for virtual machines using the CLI

The following provides information about creating directory-based storage pools and storage volumes, and assigning volumes to virtual machines.

11.2.2.1.1. Creating directory-based storage pools using the CLI

The following provides instructions for creating directory-based storage pools.

Prerequisites

  • Ensure your hypervisor supports directory storage pools: 

    # virsh pool-capabilities | grep "'dir' supported='yes'"

    If the command displays any output, directory pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create a directory-type storage pool. For example, to create a storage pool named guest_images_dir that uses the /guest_images directory: 

    # virsh pool-define-as guest_images_dir dir --target "/guest_images"
Pool guest_images_dir defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.1.2, “Directory-based storage pool parameters”.

  2. Create the storage pool target path

    Use the virsh pool-build command to create a storage pool target path for a pre-formatted file system storage pool, initialize the storage source device, and define the format of the data. 

    # virsh pool-build guest_images_dir
  Pool guest_images_dir built

# ls -la /guest_images
  total 8
  drwx------.  2 root root 4096 May 31 19:38 .
  dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..

  3. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_dir     inactive   no

  4. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_dir
  Pool guest_images_dir started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  5. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_dir
  Pool guest_images_dir marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_dir     inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. 

    # virsh pool-info guest_images_dir
  Name:           guest_images_dir
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.1.2. Directory-based storage pool parameters

This section provides information about the required XML parameters for a directory-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_dir

Parameters

The following table provides a list of required parameters for the XML file for a directory-based storage pool.

Table 11.1. Directory-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='dir'>

The name of the storage pool

<name>name</name>

The path specifying the target. This will be the path used for the storage pool.

<target>
   <path>target_path</path>
</target>

Example

The following is an example of an XML file for a storage pool based on the /guest_images directory: 

<pool type='dir'>
  <name>dirpool</name>
  <target>
    <path>/guest_images</path>
  </target>
</pool>

Additional resources

For more information on creating directory-based storage pools, see Section 11.2.2.1.1, “Creating directory-based storage pools using the CLI”.

11.2.2.2. Creating and assigning disk-based storage for virtual machines using the CLI

The following provides information about creating disk-based storage pools and storage volumes and assigning volumes to virtual machines.

11.2.2.2.1. Creating disk-based storage pools using the CLI

The following provides instructions for creating disk-based storage pools.

Recommendations

Be aware of the following before creating a disk-based storage pool:

  • Depending on the version of libvirt being used, dedicating a disk to a storage pool may reformat and erase all data currently stored on the disk device. It is strongly recommended that you back up the data on the storage device before creating a storage pool.

  • VMs should not be given write access to whole disks or block devices (for example, /dev/sdb). Use partitions (for example, /dev/sdb1) or LVM volumes.

    If you pass an entire block device to a VM, the VM will likely partition it or create its own LVM groups on it. This can cause the host machine to detect these partitions or LVM groups and cause errors.

Prerequisites

  • Ensure your hypervisor supports disk-based storage pools: 

    # virsh pool-capabilities | grep "'disk' supported='yes'"

    If the command displays any output, disk-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create a disk-type storage pool. For example, to create a storage pool named guest_images_disk that uses the /dev/sdb1 partition, and is mounted on the /dev directory: 

    # virsh pool-define-as guest_images_disk disk gpt --source-dev=/dev/sdb1 --target /dev
Pool guest_images_disk defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.2.2, “Disk-based storage pool parameters”.

  2. Create the storage pool target path

    Use the virsh pool-build command to create a storage pool target path for a pre-formatted file-system storage pool, initialize the storage source device, and define the format of the data. 

    # virsh pool-build guest_images_disk
  Pool guest_images_disk built
    Note

    Building the target path is only necessary for disk-based, file system-based, and logical storage pools. If libvirt detects that the source storage device’s data format differs from the selected storage pool type, the build fails, unless the overwrite option is specified.

  3. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_disk    inactive   no

  4. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_disk
  Pool guest_images_disk started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  5. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_disk
  Pool guest_images_disk marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_disk    inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. 

    # virsh pool-info guest_images_disk
  Name:           guest_images_disk
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.2.2. Disk-based storage pool parameters

This section provides information about the required XML parameters for a disk-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_disk

Parameters

The following table provides a list of required parameters for the XML file for a disk-based storage pool.

Table 11.2. Disk-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='disk'>

The name of the storage pool

<name>name</name>

The path specifying the storage device. For example, /dev/sdb.

<source>
   <path>source_path</path>
</source>

The path specifying the target device. This will be the path used for the storage pool.

<target>
   <path>target_path</path>
</target>

Example

The following is an example of an XML file for a disk-based storage pool: 

<pool type='disk'>
  <name>phy_disk</name>
  <source>
    <device path='/dev/sdb'/>
    <format type='gpt'/>
  </source>
  <target>
    <path>/dev</path>
  </target>
</pool>

Additional resources

For more information on creating disk-based storage pools, see Section 11.2.2.2.1, “Creating disk-based storage pools using the CLI”.

11.2.2.3. Creating and assigning filesystem-based storage for virtual machines using the CLI

The following provides information about creating filesystem-based storage pools and storage volumes, and assigning volumes to virtual machines.

11.2.2.3.1. Creating filesystem-based storage pools using the CLI

The following provides instructions for creating filesystem-based storage pools.

Recommendations

Do not use this procedure to assign an entire disk as a storage pool (for example, /dev/sdb). VMs should not be given write access to whole disks or block devices. This method should only be used to assign partitions (for example, /dev/sdb1) to storage pools.

Prerequisites

  • Ensure your hypervisor supports filesystem-based storage pools: 

    # virsh pool-capabilities | grep "'fs' supported='yes'"

    If the command displays any output, file-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create a filesystem-type storage pool. For example, to create a storage pool named guest_images_fs that uses the /dev/sdc1 partition, and is mounted on the /guest_images directory: 

    # virsh pool-define-as guest_images_fs fs --source-dev /dev/sdc1 --target /guest_images
Pool guest_images_fs defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.3.2, “Filesystem-based storage pool parameters”.

  2. Define the storage pool target path

    Use the virsh pool-build command to create a storage pool target path for a pre-formatted file-system storage pool, initialize the storage source device, and define the format of the data. 

    # virsh pool-build guest_images_fs
  Pool guest_images_fs built

# ls -la /guest_images
  total 8
  drwx------.  2 root root 4096 May 31 19:38 .
  dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..

  3. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_fs      inactive   no

  4. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_fs
  Pool guest_images_fs started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  5. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_fs
  Pool guest_images_fs marked as autostarted

  6. Verify the Autostart state

    Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_fs      inactive   yes

  7. Verify the storage pool

    Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. Verify there is a lost+found directory in the target path on the file system, indicating that the device is mounted. 

    # virsh pool-info guest_images_fs
  Name:           guest_images_fs
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB

# mount | grep /guest_images
  /dev/sdc1 on /guest_images type ext4 (rw)

# ls -la /guest_images
  total 24
  drwxr-xr-x.  3 root root  4096 May 31 19:47 .
  dr-xr-xr-x. 25 root root  4096 May 31 19:38 ..
  drwx------.  2 root root 16384 May 31 14:18 lost+found
11.2.2.3.2. Filesystem-based storage pool parameters

The following provides information about the required parameters for a filesystem-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_fs

Parameters

The following table provides a list of required parameters for the XML file for a filesystem-based storage pool.

Table 11.3. Filesystem-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='fs'>

The name of the storage pool

<name>name</name>

The path specifying the partition. For example, /dev/sdc1

<source>
   <device path=device_path />

The file system type, for example ext4.

    <format type=fs_type />
</source>

The path specifying the target. This will be the path used for the storage pool.

<target>
    <path>path-to-pool</path>
</target>

Example

The following is an example of an XML file for a storage pool based on the /dev/sdc1 partition: 

<pool type='fs'>
  <name>guest_images_fs</name>
  <source>
    <device path='/dev/sdc1'/>
    <format type='auto'/>
  </source>
  <target>
    <path>/guest_images</path>
  </target>
</pool>

Additional resources

For more information on creating filesystem-based storage pools, see Section 11.2.2.3.1, “Creating filesystem-based storage pools using the CLI”.

11.2.2.4. Creating and assigning GlusterFS storage for virtual machines using the CLI

The following provides information about creating GlusterFS-based storage pools and storage volumes, and assigning volumes to virtual machines.

11.2.2.4.1. Creating GlusterFS-based storage pools using the CLI

GlusterFS is a user space file system that uses File System in Userspace (FUSE). The following provides instructions for creating GlusterFS-based storage pools.

Prerequisites

  • Before you can create GlusterFS-based storage pool on a host, prepare a Gluster.

    1. Obtain the IP address of the Gluster server by listing its status with the following command: 

      # gluster volume status
Status of volume: gluster-vol1
Gluster process                           Port	Online	Pid
------------------------------------------------------------
Brick 222.111.222.111:/gluster-vol1       49155	  Y    18634

Task Status of Volume gluster-vol1
------------------------------------------------------------
There are no active volume tasks
    2. If not installed, install the glusterfs-fuse package.

    3. If not enabled, enable the virt_use_fusefs boolean. Check that it is enabled. 

      # setsebool virt_use_fusefs on
# getsebool virt_use_fusefs
virt_use_fusefs --> on

  • Ensure your hypervisor supports GlusterFS-based storage pools: 

    # virsh pool-capabilities | grep "'gluster' supported='yes'"

    If the command displays any output, GlusterFS-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create a GlusterFS-based storage pool. For example, to create a storage pool named guest_images_glusterfs that uses a Gluster server named gluster-vol1 with IP 111.222.111.222, and is mounted on the root directory of the Gluster server: 

    # virsh pool-define-as --name guest_images_glusterfs --type gluster --source-host 111.222.111.222 --source-name gluster-vol1 --source-path /
Pool guest_images_glusterfs defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.4.2, “GlusterFS-based storage pool parameters”.

  2. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                    State      Autostart
  --------------------------------------------
  default                 active     yes
  guest_images_glusterfs  inactive   no

  3. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_glusterfs
  Pool guest_images_glusterfs started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  4. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_glusterfs
  Pool guest_images_glusterfs marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                    State      Autostart
  --------------------------------------------
  default                 active     yes
  guest_images_glusterfs  inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. 

    # virsh pool-info guest_images_glusterfs
  Name:           guest_images_glusterfs
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.4.2. GlusterFS-based storage pool parameters

The following provides information about the required parameters for a GlusterFS-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_glusterfs

Parameters

The following table provides a list of required parameters for the XML file for a GlusterFS-based storage pool.

Table 11.4. GlusterFS-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='gluster'>

The name of the storage pool

<name>name</name>

The hostname or IP address of the Gluster server

<source>
   <name=gluster-name />

The path on the Gluster server used for the storage pool.

    <dir path=gluster-path />
</source>

Example

The following is an example of an XML file for a storage pool based on the Gluster file system at 111.222.111.222: 

<pool type='gluster'>
  <name>Gluster_pool</name>
  <source>
    <host name='111.222.111.222'/>
    <dir path='/'/>
    <name>gluster-vol1</name>
  </source>
</pool>

For more information on creating filesystem-based storage pools, see Section 11.2.2.4.1, “Creating GlusterFS-based storage pools using the CLI”.

11.2.2.5. Creating and assigning iSCSI-based storage for virtual machines using the CLI

The following provides information about creating iSCSI-based storage pools and storage volumes, securing iSCSI-based storage pools with libvirt secrets, and assigning volumes to virtual machines.

Recommendations

Internet Small Computer System Interface (iSCSI) is a network protocol for sharing storage devices. iSCSI connects initiators (storage clients) to targets (storage servers) using SCSI instructions over the IP layer.

Using iSCSI-based devices to store virtual machines allows for more flexible storage options, such as using iSCSI as a block storage device. The iSCSI devices use a Linux-IO (LIO) target. This is a multi-protocol SCSI target for Linux. In addition to iSCSI, LIO also supports Fibre Channel and Fibre Channel over Ethernet (FCoE).

If you need to prevent access to an iSCSI storage pool, you can secure it using a libvirt secret.

Prerequisites

  • Before you can create an iSCSI-based storage pool, you must create iSCSI targets. You can create iSCSI targets are created using the targetcli package, which provides a command set for creating software-backed iSCSI targets.

    For more information and instructions on creating iSCSI targets, see the Managing storage devices document.

11.2.2.5.1. Creating iSCSI-based storage pools using the CLI

The following provides instructions for creating iSCSI-based storage pools.

Prerequisites

  • Ensure your hypervisor supports iSCSI-based storage pools: 

    # virsh pool-capabilities | grep "'iscsi' supported='yes'"

    If the command displays any output, iSCSI-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create an iSCSI-type storage pool. For example, to create a storage pool named guest_images_iscsi that uses the iqn.2010-05.com.example.server1:iscsirhel7guest IQN on the server1.example.com, and is mounted on the /dev/disk/by-path path: 

    # virsh pool-define-as --name guest_images_iscsi --type iscsi --source-host server1.example.com --source-dev iqn.2010-05.com.example.server1:iscsirhel7guest --target /dev/disk/by-path
Pool guest_images_iscsi defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.5.2, “iSCSI-based storage pool parameters”.

  2. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_iscsi   inactive   no

  3. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_iscsi
  Pool guest_images_iscsi started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  4. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_iscsi
  Pool guest_images_iscsi marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_iscsi   inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. Verify there is a lost+found directory in the target path on the file system, indicating that the device is mounted. 

    # virsh pool-info guest_images_iscsi
  Name:           guest_images_iscsi
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.5.2. iSCSI-based storage pool parameters

The following provides information about the required parameters for an iSCSI-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_iscsi

Parameters

The following table provides a list of required parameters for the XML file for an iSCSI-based storage pool.

Table 11.5. iSCSI-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='iscsi'>

The name of the storage pool

<name>name</name>

The name of the host

<source>
  <host name=hostname />

The iSCSI IQN

    <device path= iSCSI_IQN />
</source>

The path specifying the target. This will be the path used for the storage pool.

<target>
   <path>/dev/disk/by-path</path>
</target>

[Optional] The IQN of the iSCSI initiator. This is only needed when the ACL restricts the LUN to a particular initiator.

<initiator>
   <iqn name='initiator0' />
</initiator>

Note

The IQN of the iSCSI initiator can be determined using the virsh find-storage-pool-sources-as iscsi command.

Example

The following is an example of an XML file for a storage pool based on the specified iSCSI device: 

<pool type='iscsi'>
  <name>iSCSI_pool</name>
  <source>
    <host name='server1.example.com'/>
    <device path='iqn.2010-05.com.example.server1:iscsirhel7guest'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
  </target>
</pool>

Additional resources

For more information on creating iSCSCI-based storage pools, see Section 11.2.2.5.1, “Creating iSCSI-based storage pools using the CLI”.

11.2.2.5.3. Securing iSCSI storage pools with libvirt secrets

User name and password parameters can be configured with virsh to secure an iSCSI storage pool. You can configure this before or after you define the pool, but the pool must be started for the authentication settings to take effect.

The following provides instructions for securing iSCSI-based storage pools with libvirt secrets.

Note

This procedure is required if a user_ID and password were defined when creating the iSCSI target.

Procedure

  1. Create a libvirt secret file with a challenge-handshake authentication protocol (CHAP) user name. For example: 

    <secret ephemeral='no' private='yes'>
    <description>Passphrase for the iSCSI example.com server</description>
    <usage type='iscsi'>
        <target>iscsirhel7secret</target>
    </usage>
</secret>

  2. Define the libvirt secret with the virsh secret-define command.

    # virsh secret-define secret.xml

  3. Verify the UUID with the virsh secret-list command. 

    # virsh secret-list
UUID                                  Usage
-------------------------------------------------------------------
2d7891af-20be-4e5e-af83-190e8a922360  iscsi iscsirhel7secret

  4. Assign a secret to the UUID in the output of the previous step using the virsh secret-set-value command. This ensures that the CHAP username and password are in a libvirt-controlled secret list. For example: 

    # virsh secret-set-value --interactive 2d7891af-20be-4e5e-af83-190e8a922360
Enter new value for secret:
Secret value set

  5. Add an authentication entry in the storage pool’s XML file using the virsh edit command, and add an <auth> element, specifying authentication type, username, and secret usage.

    For example: 

    <pool type='iscsi'>
  <name>iscsirhel7pool</name>
    <source>
       <host name='192.168.122.1'/>
       <device path='iqn.2010-05.com.example.server1:iscsirhel7guest'/>
       <auth type='chap' username='redhat'>
          <secret usage='iscsirhel7secret'/>
       </auth>
    </source>
  <target>
    <path>/dev/disk/by-path</path>
  </target>
</pool>
    Note

    The <auth> sub-element exists in different locations within the virtual machine’s <pool> and <disk> XML elements. For a <pool>, <auth> is specified within the <source> element, as this describes where to find the pool sources, since authentication is a property of some pool sources (iSCSI and RBD). For a <disk>, which is a sub-element of a domain, the authentication to the iSCSI or RBD disk is a property of the disk. In addition, the <auth> sub-element for a disk differs from that of a storage pool. 

    <auth username='redhat'>
  <secret type='iscsi' usage='iscsirhel7secret'/>
</auth>

  6. To activate the changes, activate the storage pool. If the pool has already been started, stop and restart the storage pool: 

    # virsh pool-destroy iscsirhel7pool
# virsh pool-start iscsirhel7pool

11.2.2.6. Creating and assigning LVM-based storage for virtual machines using the CLI

The following provides information about creating LVM-based storage pools and storage volumes and assigning volumes to virtual machines.

11.2.2.6.1. Creating LVM-based storage pools using the CLI

The following provides instructions for creating LVM-based storage pools.

Recommendations

Be aware of the following before creating an LVM-based storage pool:

  • LVM-based storage pools do not provide the full flexibility of LVM.
  • libvirt supports thin logical volumes, but does not provide the features of thin storage pools.

  • LVM-based storage pools are volume groups. You can create volume groups using Logical Volume Manager commands or virsh commands. To manage volume groups using the virsh interface, use the virsh commands to create volume groups.

    For more information about volume groups, refer to the Red Hat Enterprise Linux Logical Volume Manager Administration Guide.

  • LVM-based storage pools require a full disk partition. If activating a new partition or device with these procedures, the partition will be formatted and all data will be erased. If using the host’s existing Volume Group (VG) nothing will be erased. It is recommended to back up the storage device before starting.

Prerequisites

  • Ensure your hypervisor supports LVM-based storage pools: 

    # virsh pool-capabilities | grep "'logical' supported='yes'"

    If the command displays any output, LVM-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create an LVM-type storage pool. For example, the following creates a storage pool named guest_images_logical that uses a libvirt_lvm LVM device mounted on /dev/sdc. The created storage pool is mounted as /dev/libvirt_lvm. 

    # virsh pool-define-as guest_images_logical logical --source-dev=/dev/sdc --source-name libvirt_lvm --target /dev/libvirt_lvm
Pool guest_images_logical defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.6.2, “LVM-based storage pool parameters”.

  2. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                   State      Autostart
  -------------------------------------------
  default                active     yes
  guest_images_logical   inactive   no

  3. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_logical
  Pool guest_images_logical started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  4. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_logical
  Pool guest_images_logical marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                   State      Autostart
  -------------------------------------------
  default                active     yes
  guest_images_logical   inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. 

    # virsh pool-info guest_images_logical
  Name:           guest_images_logical
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.6.2. LVM-based storage pool parameters

The following provides information about the required parameters for an LVM-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_logical

Parameters

The following table provides a list of required parameters for the XML file for a LVM-based storage pool.

Table 11.6. LVM-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='logical'>

The name of the storage pool

<name>name</name>

The path to the device for the storage pool

<source>
   <device path='device_path' />`

The name of the volume group

    <name>VG-name</name>

The virtual group format

    <format type='lvm2' />
</source>

The target path

<target>
   <path=target_path />
</target>

Note

If the logical volume group is made of multiple disk partitions, there may be multiple source devices listed. For example: 

<source>
  <device path='/dev/sda1'/>
  <device path='/dev/sdb3'/>
  <device path='/dev/sdc2'/>
  ...
</source>

Example

The following is an example of an XML file for a storage pool based on the specified LVM: 

<pool type='logical'>
  <name>guest_images_lvm</name>
  <source>
    <device path='/dev/sdc'/>
    <name>libvirt_lvm</name>
    <format type='lvm2'/>
  </source>
  <target>
    <path>/dev/libvirt_lvm</path>
  </target>
</pool>

Additional resources

For more information on creating iSCSCI-based storage pools, see Section 11.2.2.6.1, “Creating LVM-based storage pools using the CLI”.

11.2.2.7. Creating and assigning network-based storage for virtual machines using the CLI

The following provides information about creating network-based storage pools and storage volumes and assigning volumes to virtual machines.

Prerequisites

  • To create a Network File System (NFS)-based storage pool, an NFS Server should already be configured to be used by the host machine. For more information about NFS, refer to the Red Hat Enterprise Linux Storage Administration Guide.
  • Ensure that the required utilities for the file system being used are installed on the host. For example, cifs-utils for Common Internet File Systems (CIFS) or glusterfs.fuse for GlusterFS.
11.2.2.7.1. Creating NFS-based storage pools using the CLI

The following provides instructions for creating storage pools based on the network file system (NFS).

Prerequisites

  • Ensure your hypervisor supports NFS-based storage pools: 

    # virsh pool-capabilities | grep "<value>nfs</value>"

    If the command displays any output, NFS-based pools are supported.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create an NFS-type storage pool. For example, to create a storage pool named guest_images_netfs that uses a NFS server with IP 111.222.111.222 mounted on the server directory /home/net_mount using the target directory /var/lib/libvirt/images/nfspool: 

    # virsh pool-define-as --name guest_images_netfs --type netfs --source-host='111.222.111.222' source-path='/home/net_mount' --source-format='nfs' --target='/var/lib/libvirt/images/nfspool'

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.7.2, “NFS-based storage pool parameters”.

  2. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_netfs   inactive   no

  3. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_netfs
  Pool guest_images_netfs started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  4. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_netfs
  Pool guest_images_netfs marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_netfs   inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. Verify there is a lost+found directory in the target path on the file system, indicating that the device is mounted. 

    # virsh pool-info guest_images_netfs
  Name:           guest_images_netfs
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.7.2. NFS-based storage pool parameters

The following provides information about the required parameters for an NFS-based storage pool and an example.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_netfs

Parameters

The following table provides a list of required parameters for the XML file for an NFS-based storage pool.

Table 11.7. NFS-based storage pool parameters

DescriptionXML

The type of storage pool

<pool type='netfs'>

The name of the storage pool

<name>name</name>

The hostname of the network server where the mount point is located. This can be a hostname or an IP address.

<source>
   <host name=hostname />

The format of the storage pool

One of the following:

    <format type='nfs' />

    <format type='glusterfs' />

    <format type='cifs' />

The directory used on the network server

    <dir path=source_path />
</source>

The path specifying the target. This will be the path used for the storage pool.

<target>
   <path>target_path</path>
</target>

Example

The following is an example of an XML file for a storage pool based on the /home/net_mount directory of the file_server NFS server: 

<pool type='netfs'>
  <name>nfspool</name>
  <source>
    <host name='file_server'/>
    <format type='nfs'/>
    <dir path='/home/net_mount'/>
  </source>
  <target>
    <path>/var/lib/libvirt/images/nfspool</path>
  </target>
</pool>

Additional resources

For more information on creating NFS-based storage pools, see Section 11.2.2.7.1, “Creating NFS-based storage pools using the CLI”.

11.2.2.8. Creating and assigning SCSI-based storage with vHBA devices for virtual machines using the CLI

The following provides information about creating SCSI-based storage pools and storage volumes using vHBA devices, as well as assigning volumes to virtual machines (VMs).

Recommendations

N_Port ID Virtualization (NPIV) is a software technology that allows sharing of a single physical Fibre Channel host bus adapter (HBA). This allows multiple VMs to see the same storage from multiple physical hosts, and thus allows for easier migration paths for the storage. As a result, there is no need for the migration to create or copy storage, as long as the correct storage path is specified.

In virtualization, the virtual host bus adapter, or vHBA, controls the Logical Unit Numbers (LUNs) for VMs. For a host to share one Fibre Channel device path between multiple VMs, you must create a vHBA for each VM. A single vHBA cannot be used by multiple VMs.

Each vHBA for NPIV is identified by its parent HBA and its own World Wide Node Name (WWNN) and World Wide Port Name (WWPN). The path to the storage is determined by the WWNN and WWPN values. The parent HBA can be defined as scsi_host# or as a WWNN/WWPN pair.

Note

If a parent HBA is defined as scsi_host# and hardware is added to the host machine, the scsi_host# assignment may change. Therefore, it is recommended that you define a parent HBA using a WWNN/WWPN pair.

It is recommended that you define a libvirt storage pool based on the vHBA, because this preserves the vHBA configuration.

Using a libvirt storage pool has two primary advantages:

  • The libvirt code can easily find the LUN’s path via virsh command output.
  • You can migrate a VM requires only defining and starting a storage pool with the same vHBA name on the target machine. To do this, the vHBA LUN, libvirt storage pool and volume name must be specified in the VM’s XML configuration.
Note

Before creating a vHBA, it is recommended that you configure storage array (SAN)-side zoning in the host LUN to provide isolation between VMs and prevent the possibility of data corruption.

To create a persistent vHBA configuration, first create a libvirt 'scsi' storage pool XML file. For information on the XML file, see Creating vHBAs. When creating a single vHBA that uses a storage pool on the same physical HBA, it is recommended to use a stable location for the <path> value, such as one of the /dev/disk/by-{path|id|uuid|label} locations on your system.

When creating multiple vHBAs that use storage pools on the same physical HBA, the value of the <path> field must be only /dev/, otherwise storage pool volumes are visible only to one of the vHBAs, and devices from the host cannot be exposed to multiple VMs with the NPIV configuration.

For more information on <path> and the elements in <target>, see upstream libvirt documentation.

11.2.2.8.1. Creating vHBAs

The following provides instructions on creating a virtual host bus adapter (vHBA).

Procedure

  1. Locate the HBAs on your host system, using the virsh nodedev-list --cap vports command.

    The following example shows a host that has two HBAs that support vHBA: 

    # virsh nodedev-list --cap vports
scsi_host3
scsi_host4

  2. View the HBA’s details, using the virsh nodedev-dumpxml HBA_device command. 

    # virsh nodedev-dumpxml scsi_host3

    The output from the command lists the <name>, <wwnn>, and <wwpn> fields, which are used to create a vHBA. <max_vports> shows the maximum number of supported vHBAs. For example: 

    <device>
  <name>scsi_host3</name>
  <path>/sys/devices/pci0000:00/0000:00:04.0/0000:10:00.0/host3</path>
  <parent>pci_0000_10_00_0</parent>
  <capability type='scsi_host'>
    <host>3</host>
    <unique_id>0</unique_id>
    <capability type='fc_host'>
      <wwnn>20000000c9848140</wwnn>
      <wwpn>10000000c9848140</wwpn>
      <fabric_wwn>2002000573de9a81</fabric_wwn>
    </capability>
    <capability type='vport_ops'>
      <max_vports>127</max_vports>
      <vports>0</vports>
    </capability>
  </capability>
</device>

    In this example, the <max_vports> value shows there are a total 127 virtual ports available for use in the HBA configuration. The <vports> value shows the number of virtual ports currently being used. These values update after creating a vHBA.

  3. Create an XML file similar to one of the following for the vHBA host. In these examples, the file is named vhba_host3.xml.

    This example uses scsi_host3 to describe the parent vHBA. 

    <device>
  <parent>scsi_host3</parent>
  <capability type='scsi_host'>
    <capability type='fc_host'>
    </capability>
  </capability>
</device>

    This example uses a WWNN/WWPN pair to describe the parent vHBA. 

    <device>
  <name>vhba</name>
  <parent wwnn='20000000c9848140' wwpn='10000000c9848140'/>
  <capability type='scsi_host'>
    <capability type='fc_host'>
    </capability>
  </capability>
</device>
    Note

    The WWNN and WWPN values must match those in the HBA details seen in the previous step.

    The <parent> field specifies the HBA device to associate with this vHBA device. The details in the <device> tag are used in the next step to create a new vHBA device for the host. For more information on the nodedev XML format, see the libvirt upstream pages.

    Note

    The virsh command does not provide a way to define the parent_wwnn, parent_wwpn, or parent_fabric_wwn attributes.

  4. Create a VHBA based on the XML file created in the previous step using the virsh nodev-create command. 

    # virsh nodedev-create vhba_host3
Node device scsi_host5 created from vhba_host3.xml

Verification

  • Verify the new vHBA’s details (scsi_host5) using the virsh nodedev-dumpxml command: 

    # virsh nodedev-dumpxml scsi_host5
<device>
  <name>scsi_host5</name>
  <path>/sys/devices/pci0000:00/0000:00:04.0/0000:10:00.0/host3/vport-3:0-0/host5</path>
  <parent>scsi_host3</parent>
  <capability type='scsi_host'>
    <host>5</host>
    <unique_id>2</unique_id>
    <capability type='fc_host'>
      <wwnn>5001a4a93526d0a1</wwnn>
      <wwpn>5001a4ace3ee047d</wwpn>
      <fabric_wwn>2002000573de9a81</fabric_wwn>
    </capability>
  </capability>
</device>
11.2.2.8.2. Creating SCSI-based storage pools with vHBA devices using the CLI

The following provides instructions for creating SCSI-based storage pools using virtual host bus adapter (vHBA) devices.

Prerequisites

  • Ensure your hypervisor supports SCSI-based storage pools: 

    # virsh pool-capabilities | grep "'scsi' supported='yes'"

    If the command displays any output, SCSI-based pools are supported.

  • Before creating a SCSI-based storage pools with vHBA devices, create a vHBA. For more information, see Creating vHBAs.

Procedure

  1. Create a storage pool

    Use the virsh pool-define-as command to define and create SCSI storage pool using a vHBA. For example, the following creates a storage pool named guest_images_vhba that uses a vHBA identified by the scsi_host3 parent adapter, world-wide port number 5001a4ace3ee047d, and world-wide node number 5001a4a93526d0a1. The storage pool is mounted on the /dev/disk/ directory: 

    # virsh pool-define-as guest_images_vhba scsi --adapter-parent scsi_host3 --adapter-wwnn 5001a4a93526d0a1 --adapter-wwpn 5001a4ace3ee047d --target /dev/disk/
Pool guest_images_vhba defined

    If you already have an XML configuration of the storage pool you want to create, you can also define the pool based on the XML. For details, see Section 11.2.2.8.3, “Parameters for SCSI-based storage pools with vHBA devices”.

  2. Verify that the pool was created

    Use the virsh pool-list command to verify that the pool was created. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_vhba    inactive   no

  3. Start the storage pool

    Use the virsh pool-start command to mount the storage pool. 

    # virsh pool-start guest_images_vhba
  Pool guest_images_vhba started
    Note

    The virsh pool-start command is only necessary for persistent storage pools. Transient storage pools are automatically started when they are created.

  4. [Optional] Turn on autostart

    By default, a storage pool defined with the virsh command is not set to automatically start each time libvirtd starts. Use the virsh pool-autostart command to configure the storage pool to autostart. 

    # virsh pool-autostart guest_images_vhba
  Pool guest_images_vhba marked as autostarted

Verification

  1. Use the virsh pool-list command to verify the Autostart state. 

    # virsh pool-list --all

  Name                 State      Autostart
  -----------------------------------------
  default              active     yes
  guest_images_vhba    inactive   yes

  2. Verify that the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. 

    # virsh pool-info guest_images_vhba
  Name:           guest_images_vhba
  UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
  State:          running
  Persistent:     yes
  Autostart:      yes
  Capacity:       458.39 GB
  Allocation:     197.91 MB
  Available:      458.20 GB
11.2.2.8.3. Parameters for SCSI-based storage pools with vHBA devices

The following provides information about the required parameters for a SCSi-based storage pool that uses a virtual host adapter bus (vHBA) device.

You can define a storage pool based on the XML configuration in a specified file. For example: 

# virsh pool-define ~/guest_images.xml
  Pool defined from guest_images_vhba

Parameters

The following table provides a list of required parameters for the XML file for a SCSI-based storage pool with vHBA.

Table 11.8. Parameters for SCSI-based storage pools with vHBA devices

DescriptionXML

The type of storage pool

<pool type='scsi'>

The name of the storage pool

<name>name</name>

The identifier of the vHBA. The parent attribute is optional.

<source>
   <adapter type='fc_host'
   [parent=parent_scsi_device]
   wwnn='WWNN'
   wwpn='WWPN' />
</source>

The target path. This will be the path used for the storage pool.

<target>
   <path=target_path />
</target>

Important

When the <path> field is /dev/, libvirt generates a unique short device path for the volume device path. For example, /dev/sdc. Otherwise, the physical host path is used. For example, /dev/disk/by-path/pci-0000:10:00.0-fc-0x5006016044602198-lun-0. The unique short device path allows the same volume to be listed in multiple virtual machines (VMs) by multiple storage pools. If the physical host path is used by multiple VMs, duplicate device type warnings may occur.

Note

The parent attribute can be used in the <adapter> field to identify the physical HBA parent from which the NPIV LUNs by varying paths can be used. This field, scsi_hostN, is combined with the vports and max_vports attributes to complete the parent identification. The parent, parent_wwnn, parent_wwpn, or parent_fabric_wwn attributes provide varying degrees of assurance that after the host reboots the same HBA is used.

  • If no parent is specified, libvirt uses the first scsi_hostN adapter that supports NPIV.
  • If only the parent is specified, problems can arise if additional SCSI host adapters are added to the configuration.
  • If parent_wwnn or parent_wwpn is specified, after the host reboots the same HBA is used.
  • If parent_fabric_wwn is used, after the host reboots an HBA on the same fabric is selected, regardless of the scsi_hostN used.

Examples

The following are examples of XML files for SCSI-based storage pools with vHBA.

  • A storage pool that is the only storage pool on the HBA: 

    <pool type='scsi'>
  <name>vhbapool_host3</name>
  <source>
    <adapter type='fc_host' wwnn='5001a4a93526d0a1' wwpn='5001a4ace3ee047d'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
  </target>
</pool>

  • A storage pool that is one of several storage pools that use a single vHBA and uses the parent attribute to identify the SCSI host device: 

    <pool type='scsi'>
  <name>vhbapool_host3</name>
  <source>
    <adapter type='fc_host' parent='scsi_host3' wwnn='5001a4a93526d0a1' wwpn='5001a4ace3ee047d'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
  </target>
</pool>

Additional resources

For more information on creating SCSI-based storage pools with vHBA, see Section 11.2.2.8.2, “Creating SCSI-based storage pools with vHBA devices using the CLI”.

11.2.2.9. Creating and assigning storage volumes using the CLI

To obtain a disk image and attach it to a virtual machine (VM) as a virtual disk, create a storage volume and assign its XML configuration to a the VM.

Prerequisites

  • A storage pool with unallocated space is present on the host. To verify, list the storage pools on the host: 

    # virsh pool-list --details

Name               State     Autostart   Persistent   Capacity     Allocation   Available
--------------------------------------------------------------------------------------------
default            running   yes         yes          48.97 GiB    36.34 GiB    12.63 GiB
Downloads          running   yes         yes          175.92 GiB   121.20 GiB   54.72 GiB
VM-disks           running   yes         yes          175.92 GiB   121.20 GiB   54.72 GiB

Procedure

  1. Create a storage volume using the virsh vol-create-as command. For example, to create a 20 GB qcow2 volume based on the guest-images-fs storage pool: 

    # virsh vol-create-as --pool guest-images-fs --name vm-disk1 --capacity 20 --format qcow2

    Important: Specific storage pool types do not support the virsh vol-create-as command and instead require specific processes to create storage volumes:

    • GlusterFS-based - Use the qemu-img command to create storage volumes.
    • iSCSI-based - Prepare the iSCSI LUNs in advance on the iSCSI server.
    • Multipath-based - Use the multipathd command to prepare or manage the multipath.
    • vHBA-based - Prepare the fibre channel card in advance.

  2. Create an XML file, and add the following lines in it. This file will be used to add the storage volume as a disk to a VM. 

    <disk type='volume' device='disk'>
    <driver name='qemu' type='qcow2'/>
    <source pool='guest-images-fs' volume='vm-disk1'/>
    <target dev='hdk' bus='ide'/>
</disk>

    This example specifies a virtual disk that uses the vm-disk1 volume, created in the previous step, and sets the volume to be set up as disk hdk on an ide bus. Modify the respective parameters as appropriate for your environment.

    Important: With specific storage pool types, you must use different XML formats to describe a storage volume disk.

    • For GlusterFS-based pools: 

        <disk type='network' device='disk'>
    <driver name='qemu' type='raw'/>
    <source protocol='gluster' name='Volume1/Image'>
      <host name='example.org' port='6000'/>
    </source>
    <target dev='vda' bus='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
  </disk>

    • For multipath-based pools: 

      <disk type='block' device='disk'>
<driver name='qemu' type='raw'/>
<source dev='/dev/mapper/mpatha' />
<target dev='sda' bus='scsi'/>
</disk>

    • For RBD-based storage pools: 

        <disk type='network' device='disk'>
    <driver name='qemu' type='raw'/>
    <source protocol='rbd' name='pool/image'>
      <host name='mon1.example.org' port='6321'/>
    </source>
    <target dev='vdc' bus='virtio'/>
  </disk>

  3. Use the XML file to assign the storage volume as a disk to a VM. For example, to assign a disk defined in ~/vm-disk1.xml to the testguest1 VM: 

    # attach-device --config testguest1 ~/vm-disk1.xml

Verification

  • In the guest operating system of the VM, confirm that the disk image has become available as an un-formatted and un-allocated disk.

11.2.3. Deleting storage for virtual machines using the CLI

The following provides information about deleting storage pools and storage volumes using the CLI.

11.2.3.1. Deleting storage pools using the CLI

To remove a storage pool from your host system, you must stop the pool and remove its XML definition.

Procedure

  1. List the defined storage pools using the virsh pool-list command. 

    # virsh pool-list --all
Name                 State      Autostart
-------------------------------------------
default              active     yes
Downloads            active     yes
RHEL8-Storage-Pool   active     yes

  2. Stop the storage pool you want to delete using the virsh pool-destroy command. 

    # virsh pool-destroy Downloads
Pool Downloads destroyed

  3. Optional: For some types of storage pools, you can remove the directory where the storage pool resides using the virsh pool-delete command. Note that to do so, the directory must be empty. 

    # virsh pool-delete Downloads
Pool Downloads deleted

  4. Delete the definition of the storage pool using the virsh pool-undefine command. 

    # virsh pool-undefine Downloads
Pool Downloads has been undefined

Verification

  • Confirm that the storage pool was deleted. 

    # virsh pool-list --all
Name                 State      Autostart
-------------------------------------------
default              active     yes
RHEL8-Storage-Pool   active     yes

11.2.3.2. Deleting storage volumes using the CLI

To remove a storage volume from your host system, you must stop the pool and remove its XML definition.

Prerequisites

  • Any virtual machine that uses the storage volume you want to delete is shut down.

Procedure

  1. List the defined storage volumes in a storage pool using the virsh vol-list command. The command must specify the name or path of a storage pool. 

    # virsh vol-list --pool RHEL8-Storage-Pool
 Name                 Path
---------------------------------------------------------------
 .bash_history        /home/VirtualMachines/.bash_history
 .bash_logout         /home/VirtualMachines/.bash_logout
 .bash_profile        /home/VirtualMachines/.bash_profile
 .bashrc              /home/VirtualMachines/.bashrc
 .git-prompt.sh       /home/VirtualMachines/.git-prompt.sh
 .gitconfig           /home/VirtualMachines/.gitconfig
 RHEL8_Volume.qcow2   /home/VirtualMachines/RHEL8_Volume.qcow2

  2. Delete storage volumes using the virsh vol-delete command. The command must specify the name or path of the storage volume and the storage pool from which the storage volume is abstracted. 

    # virsh vol-delete --pool RHEL-Storage-Pool RHEL8_Volume.qcow2
Pool RHEL8_Volume.qcow2 deleted

Verification

  • List the defined storage volumes again, and check that the output no longer displays the deleted volume. 

    # virsh vol-list --pool RHEL8-Storage-Pool
 Name                 Path
---------------------------------------------------------------
 .bash_history        /home/VirtualMachines/.bash_history
 .bash_logout         /home/VirtualMachines/.bash_logout
 .bash_profile        /home/VirtualMachines/.bash_profile
 .bashrc              /home/VirtualMachines/.bashrc
 .git-prompt.sh       /home/VirtualMachines/.git-prompt.sh
 .gitconfig           /home/VirtualMachines/.gitconfig

11.3. Managing storage for virtual machines using the web console

Using the RHEL 8 web console, you can manage various aspects of a virtual machine’s (VM’s) storage. You can use the web console to:

11.3.1. Viewing storage pool information using the web console

The following procedure describes how to view detailed storage pool information about the virtual machine (VM) storage pools that the web console session can access.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines interface. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

    The information includes the following:

    • Name - The name of the storage pool.
    • Size - The size of the storage pool.
    • Connection - The connection used to access the storage pool.
    • State - The state of the storage pool.

  2. Click the row of the storage whose information you want to see.

    The row expands to reveal the Overview pane with the following information about the selected storage pool:

    • Path - The path to the storage pool.
    • Persistent - Whether or not the storage pool is persistent.
    • Autostart - Whether or not the storage pool starts automatically.
    • Type - The type of the storage pool.
    web console storage pool overview

  3. To view a list of storage volumes created from the storage pool, click Storage Volumes.

    The Storage Volumes pane appears, showing a list of configured storage volumes with their sizes and the amount of space used.

    web console storage pool storage volumes

Additional resources

11.3.2. Creating storage pools using the web console

A virtual machine (VM) requires a file, directory, or storage device that can be used to create storage volumes to store the VM image or act as additional storage. You can create storage pools from local or network-based resources that you can then use to create the storage volumes.

To create storage pools using the RHEL web console, see the following procedure.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines tab. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

  2. Click Create Storage Pool. The Create Storage Pool dialog appears.

    cockpit create storage pool

  3. Enter the following information in the Create Storage Pool dialog:

    • Name - The name of the storage pool.
    • Type - The type of the storage pool. This can be a file-system directory, a network file system, an iSCSI target, a physical disk drive, or an LVM volume group.
    • Target Path - The storage pool path on the host’s file system.
    • Startup - Whether or not the storage pool starts when the host boots.
  4. Click Create. The storage pool is created, the Create Storage Pool dialog closes, and the new storage pool appears in the list of storage pools.

Additional resources

11.3.3. Removing storage pools using the web console

You can remove storage pools to free up resources on the host or on the network to improve system performance. Deleting storage pools also frees up resources that can then be used by other virtual machines (VMs).

Important

Unless explicitly specified, deleting a storage pool does not simultaneously delete the storage volumes inside that pool.

To delete a storage pool using the RHEL web console, see the following procedure.

Note

If you want to temporarily deactivate a storage pool instead of deleting it, see Deactivating storage pools using the web console

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines tab. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

  2. In the Storage Pools window, click the storage pool you want to delete.

    The row expands to reveal the Overview pane with basic information about the selected storage pool and controls for deactivating or deleting the storage pool.

    web console storage pool overview

  3. Click Delete.

    A confirmation dialog appears.

    cockpit storage pool delete confirm
  4. Optional: To delete the storage volumes inside the pool, select the check box in the dialog.

  5. Click Delete.

    The storage pool is deleted. If you had selected the checkbox in the previous step, the associated storage volumes are deleted as well.

Additional resources

11.3.4. Deactivating storage pools using the web console

If you do not want to permanently delete a storage pool, you can temporarily deactivate it instead.

When you deactivate a storage pool, no new volumes can be created in that pool. However, any virtual machines (VMs) that have volumes in that pool will continue to run. This is useful for a number of reasons, for example, you can limit the number of volumes that can be created in a pool to increase system performance.

To deactivate a storage pool using the RHEL web console, see the following procedure.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines tab. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

  2. In the Storage Pools window, click the storage pool you want to deactivate.

    The row expands to reveal the Overview pane with basic information about the selected storage pool and controls for deactivating and deleting the VM.

    web console storage pool overview

  3. Click Deactivate.

    web console storage pool overview

    The storage pool is deactivated.

Additional resources

11.3.5. Creating storage volumes using the web console

To create a functioning virtual machine (VM) you require a local storage device assigned to the VM that can store the VM image and VM-related data. You can create a storage volume in a storage pool and assign it to a VM as a storage disk.

To create storage volumes using the web console, see the following procedure.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines tab. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

  2. In the Storage Pools window, click the storage pool from which you want to create a storage volume.

    The row expands to reveal the Overview pane with basic information about the selected storage pool.

    web console storage pool overview

  3. Click Storage Volumes next to the Overview tab in the expanded row.

    The Storage Volume tab appears with basic information about existing storage volumes, if any.

    cockpit storage volume overview

  4. Click Create Volume.

    The Create Storage Volume dialog appears.

    cockpit create storage volume

  5. Enter the following information in the Create Storage Volume dialog:

    • Name - The name of the storage volume.
    • Size - The size of the storage volume in MiB or GiB.
    • Format - The format of the storage volume. The supported types are qcow2 and raw.

  6. Click Create.

    The storage volume is created, the Create Storage Volume dialog closes, and the new storage volume appears in the list of storage volumes.

Additional resources

11.3.6. Removing storage volumes using the web console

You can remove storage volumes to free up space in the storage pool, or to remove storage items associated with defunct virtual machines (VMs).

To remove storage volumes using the RHEL web console, see the following procedure.

Prerequisites

Procedure

  1. Click Storage Pools at the top of the Virtual Machines tab. The Storage Pools window appears, showing a list of configured storage pools.

    web console storage pools window

  2. In the Storage Pools window, click the storage pool from which you want to remove a storage volume.

    The row expands to reveal the Overview pane with basic information about the selected storage pool.

    web console storage pool overview

  3. Click Storage Volumes next to the Overview tab in the expanded row.

    The Storage Volume tab appears with basic information about existing storage volumes, if any.

    cockpit storage volume overview

  4. Select the storage volume you want to remove.

    cockpit delete storage volume
  5. Click Delete 1 Volume

Additional resources

11.3.7. Managing virtual machine disks using the web console

Using the RHEL 8 web console, you can manage the disks configured for the virtual machines to which the web console is connected.

You can:

11.3.7.1. Viewing virtual machine disk information in the web console

The following procedure describes how to view the disk information of a virtual machine (VM) to which the web console session is connected.

Prerequisites

To use the web console to manage VMs, install the web console VM plug-in.

Procedure

  1. Click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Disks.

    The Disks pane appears with information about the disks assigned to the VM.

cockpit disk info

The information includes the following:

  • Device - The device type of the disk.
  • Used - The amount of the disk that is used.
  • Capacity - The size of the disk.
  • Bus - The bus type of the disk.
  • Access - Whether the disk is is writeable or read-only.
  • Source - The disk device or file.

Additional resources

11.3.7.2. Adding new disks to virtual machines using the web console

You can add new disks to virtual machines (VMs) by creating a new storage volume and attaching it to a VM using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM for which you want to create and attach a new disk.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Disks.

    The Disks pane appears with information about the disks configured for the VM.

    cockpit disk info

  3. Click Add Disk.

    The Add Disk dialog appears.

    cockpit add disk

  4. Select the Create New option.

  5. Configure the new disk.

    • Pool - Select the storage pool from which the virtual disk will be created.
    • Name - Enter a name for the virtual disk that will be created.
    • Size - Enter the size and select the unit (MiB or GiB) of the virtual disk that will be created.
    • Format - Select the format for the virtual disk that will be created. The supported types are qcow2 and raw.

    • Persistence - If checked, the virtual disk is persistent. If not checked, the virtual disk is transient.

      Note

      Transient disks can only be added to VMs that are running.

    • Additional Options - Set additional configurations for the virtual disk.

      • Cache - Select the type of cache for the virtual disk.
      • Bus - Select the type of bus for the virtual disk.

  6. Click Add.

    The virtual disk is created and connected to the VM.

Additional resources

11.3.7.3. Attaching existing disks to virtual machines using the web console

The following procedure describes how to attach existing storage volumes as disks to a virtual machine (VM) using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM to which you want to attach an existing disk.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Disks.

    The Disks pane appears with information about the disks configured for the VM.

    cockpit disk info

  3. Click Add Disk.

    The Add Disk dialog appears.

    cockpit add disk

  4. Click the Use Existing radio button.

    The appropriate configuration fields appear in the Add Disk dialog.

    cockpit attach disk

  5. Configure the disk for the VM.

    • Pool - Select the storage pool from which the virtual disk will be attached.
    • Volume - Select the storage volume that will be attached.
    • Persistence - Check to make the virtual disk persistent. Clear to make the virtual disk transient.

    • Additional Options - Set additional configurations for the virtual disk.

      • Cache - Select the type of cache for the virtual disk.
      • Bus - Select the type of bus for the virtual disk.

  6. Click Add

    The selected virtual disk is attached to the VM.

Additional resources

11.3.7.4. Detaching disks from virtual machines

The following describes how to detach disks from virtual machines (VMs) using the RHEL 8 web console.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM from which you want to detach an existing disk.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Disks.

    The Disks pane appears with information about the disks configured for the VM.

    cockpit disk info

  3. Click the Remove button next to the disk you want to detach from the VM. A Remove Disk confirmation dialog appears.

  4. In the confirmation dialog, click Remove.

    The virtual disk is detached from the VM.

Additional resources

Chapter 12. Managing NVIDIA vGPU devices

The vGPU feature makes it possible to divide a physical NVIDIA GPU device into multiple virtual devices, referred to as mediated devices. These mediated devices can then be assigned to multiple virtual machines (VMs) as virtual GPUs. As a result, these VMs can share the performance of a single physical GPU.

Important

Assigning a physical GPU to VMs, with or without using mediated devices, makes it impossible for the host to use the GPU.

12.1. Setting up NVIDIA vGPU devices

To set up the NVIDIA vGPU feature, you need to download NVIDIA vGPU drivers for your GPU device, create mediated devices, and assign them to the intended virtual machines. For detailed instructions, see below.

Prerequisites

  • The mdevctl package is installed. 

    # yum install mdevctl

  • Your GPU supports vGPU mediated devices. For an up-to-date list of NVIDIA GPUs that support creating vGPUs, see the NVIDIA GPU Software Documentation.

    • If you do not know which GPU your host is using, install the lshw package and use the lshw -C display command. The following example shows the system is using an NVIDIA Tesla P4 GPU, compatible with vGPU. 

      # lshw -C display

*-display
       description: 3D controller
       product: GP104GL [Tesla P4]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress cap_list
       configuration: driver=vfio-pci latency=0
       resources: irq:16 memory:f6000000-f6ffffff memory:e0000000-efffffff memory:f0000000-f1ffffff

Procedure

  1. Download the NVIDIA vGPU drivers and install them on your system. For instructions, see the NVIDIA documentation.

  2. If the NVIDIA software installer did not create the /etc/modprobe.d/nvidia-installer-disable-nouveau.conf file, create a conf file of any name in /etc/modprobe.d/, and add the following lines in the file: 

    blacklist nouveau
options nouveau modeset=0

  3. Regenerate the initial ramdisk for the current kernel, then reboot. 

    # dracut --force
# reboot

  4. Check that the kernel has loaded the nvidia_vgpu_vfio module and that the nvidia-vgpu-mgr.service service is running. 

    # lsmod | grep nvidia_vgpu_vfio
nvidia_vgpu_vfio 45011 0
nvidia 14333621 10 nvidia_vgpu_vfio
mdev 20414 2 vfio_mdev,nvidia_vgpu_vfio
vfio 32695 3 vfio_mdev,nvidia_vgpu_vfio,vfio_iommu_type1

# systemctl status nvidia-vgpu-mgr.service
nvidia-vgpu-mgr.service - NVIDIA vGPU Manager Daemon
   Loaded: loaded (/usr/lib/systemd/system/nvidia-vgpu-mgr.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2018-03-16 10:17:36 CET; 5h 8min ago
 Main PID: 1553 (nvidia-vgpu-mgr)
 [...]

  5. Generate a device UUID. 

    # uuidgen
30820a6f-b1a5-4503-91ca-0c10ba58692a

  6. Create a mediated device from the GPU hardware that you detected in the prerequisites, and assign the generated UUID to the device.

    The following example shows how to create a mediated device of the nvidia-63 vGPU type on an NVIDIA Tesla P4 card that runs on the 0000:01:00.0 PCI bus: 

    # mdevctl start -u 30820a6f-b1a5-4503-91ca-0c10ba58692a -p 0000:01:00.0 --type nvidia-63
    Note

    For the vGPU type values for specific GPU devices, see the Virtual GPU software documentation.

  7. Make the mediated device persistent: 

    # mdevctl define --auto --uuid 30820a6f-b1a5-4503-91ca-0c10ba58692a

  8. Attach the mediated device to a VM that you want to share the vGPU resources. To do so, add the following lines, along with the previously genereated UUID, to the <devices/> sections in the XML configuration of the VM. 

    <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci'>
  <source>
    <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/>
  </source>
</hostdev>

    Note that each UUID can only be assigned to one VM at a time.

  9. For full functionality of the vGPU mediated devices to be available on the assigned VMs, set up NVIDIA vGPU guest software licensing on the VMs. For further information and instructions, see the NVIDIA Virtual GPU Software License Server User Guide.

Verification

  • List the active mediated devices on your host. If the output displays a defined device with the UUID used in the procedure, NVIDIA vGPU has been configured correctly. For example: 

    # mdevctl list
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63
30820a6f-b1a5-4503-91ca-0c10ba58692a 0000:01:00.0 nvidia-63 (defined)

Additional resources

  • For more information on using the mdevctl utility, use man mdevctl.

12.2. Removing NVIDIA vGPU devices

To change the configuration of assigned vGPU mediated devices, you need to remove the existing devices from the assigned VMs. For instructions, see below:

Prerequisites

  • The mdevctl package is installed. 

    # yum install mdevctl
  • The VM from which you want to remove the device is shut down.

Procedure

  1. Obtain the UUID of the mediated device that you want to remove. To do so, use the mdevctl list command: 

    # mdevctl list
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63 (defined)
30820a6f-b1a5-4503-91ca-0c10ba58692a 0000:01:00.0 nvidia-63 (defined)

  2. Stop the running instance of the mediated vGPU device. To do so, use the mdevctl stop command with the UUID of the device. For example, to stop the 30820a6f-b1a5-4503-91ca-0c10ba58692a device: 

    # mdevctl stop -u 30820a6f-b1a5-4503-91ca-0c10ba58692a

  3. Remove the device from the XML configuration of the VM. To do so, use the virsh edit utility to edit the XML configuration of the VM, and remove the mdev’s configuration segment. The segment will look similar to the following: 

    <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci'>
  <source>
    <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/>
  </source>
</hostdev>

    Note that stopping and detaching the mediated device does not delete it, but rather keeps it as defined. As such, you can restart and attach the device to a different VM.

  4. Optional: To delete the stopped mediated device, remove its definition: 

    # mdevctl undefine -u 30820a6f-b1a5-4503-91ca-0c10ba58692a

Verification

  • If you only stopped and detached the device, list the active mediated devices and the defined mediated devices. 

    # mdevctl list
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63 (defined)
# mdevctl list --defined
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63 auto (active)
30820a6f-b1a5-4503-91ca-0c10ba58692a 0000:01:00.0 nvidia-63 manual

    If the first command does not display the device but the second command does, the procedure was successful.

  • If you also deleted the device, the second command should not display the device. 

    # mdevctl list
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63 (defined)
# mdevctl list --defined
85006552-1b4b-45ef-ad62-de05be9171df 0000:01:00.0 nvidia-63 auto (active)

Additional resources

  • For more information on using the mdevctl utility, use man mdevctl.

12.3. Obtaining NVIDIA vGPU information about your system

To evaluate the capabilities of the vGPU features available to you, you can obtain additional information about the mediated devices on your system, such as:

  • How many mediated devices of a given type can be created
  • What mediated devices are already configured on your system.

Prerequisites

  • The mdevctl package is installed. 

    # yum install mdevctl

Procedure

  • To see the available vGPU types on your host, use the mdevctl types command.

    For example, the following shows the information for a system that uses a physical Tesla T4 card under the 0000:41:00.0 PCI bus: 

    # mdevctl types
0000:41:00.0
  nvidia-222
    Available instances: 0
    Device API: vfio-pci
    Name: GRID T4-1B
    Description: num_heads=4, frl_config=45, framebuffer=1024M, max_resolution=5120x2880, max_instance=16
  nvidia-223
    Available instances: 0
    Device API: vfio-pci
    Name: GRID T4-2B
    Description: num_heads=4, frl_config=45, framebuffer=2048M, max_resolution=5120x2880, max_instance=8
  nvidia-224
    Available instances: 0
    Device API: vfio-pci
    Name: GRID T4-2B4
    Description: num_heads=4, frl_config=45, framebuffer=2048M, max_resolution=5120x2880, max_instance=8
  nvidia-225
    Available instances: 0
    Device API: vfio-pci
    Name: GRID T4-1A
    Description: num_heads=1, frl_config=60, framebuffer=1024M, max_resolution=1280x1024, max_instance=16
    [...]

  • To see the active vGPU devices on your host, including their types, UUIDs, and PCI buses of parent devices, use the mdevctl list command: 

    # mdevctl list
85006552-1b4b-45ef-ad62-de05be9171df 0000:41:00.0 nvidia-223
83c32df7-d52e-4ec1-9668-1f3c7e4df107 0000:41:00.0 nvidia-223 (defined)

    This example shows that the 85006552-1b4b-45ef-ad62-de05be9171df device is running but not defined, and the 83c32df7-d52e-4ec1-9668-1f3c7e4df107 is both defined and running.

Additional resources

  • For more information on using the mdevctl utility, use man mdevctl.

12.4. Remote desktop streaming services for NVIDIA vGPU

The following remote desktop streaming services have been successfully tested for use with the NVIDIA vGPU feature in RHEL 8 hosts:

  • HP-RGS - Note that it is currently not possible to use HP-RGS with RHEL 8 VMs.
  • Mechdyne TGX - Note that it is currently not possible to use Mechdyne TGX with Windows Server 2016 VMs.
  • NICE DCV - When using this streaming service, Red Hat recommends using fixed resolution settings, as using dynamic resolution in some cases results in a black screen. In addition, it is currently not possible to use NICE DCV with RHEL 8 VMs.

Chapter 13. Configuring virtual machine network connections

For your virtual machines (VMs) to connect over a network to your host, to other VMs on your host, and to locations on an external network, the VM networking must be configured accordingly. To provide VM networking, the RHEL 8 hypervisor and newly created VMs have a default network configuration, which can also be modified further. For example:

  • You can enable the VMs on your host to be discovered and connected to by locations outside the host, as if the VMs were on the same network as the host.
  • You can partially or completely isolate a VM from inbound network traffic to increase its security and minimize the risk of any problems with the VM impacting the host.

The following sections explain the various types of VM network configuration and provide instructions for setting up selected VM network configurations.

13.1. Understanding virtual networking

The connection of virtual machines (VMs) to other devices and locations on a network has to be facilitated by the host hardware. The following sections explain the mechanisms of VM network connections and describe the default VM network setting.

13.1.1. How virtual networks work

Virtual networking uses the concept of a virtual network switch. A virtual network switch is a software construct that operates on a host machine. VMs connect to the network through the virtual network switch. Based on the configuration of the virtual switch, a VM can use use an existing virtual network managed by the hypervisor, or a different network connection method.

The following figure shows a virtual network switch connecting two VMs to the network:

vn 02 switchandtwoguests

From the perspective of a guest operating system, a virtual network connection is the same as a physical network connection. Host machines view virtual network switches as network interfaces. When the libvirtd service is first installed and started, it creates virbr0, the default network interface for VMs.

To view information about this interface, use the ip utility on the host. 

$ ip addr show virbr0
3: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state
 UNKNOWN link/ether 1b:c4:94:cf:fd:17 brd ff:ff:ff:ff:ff:ff
 inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

By default, all VMs on a single host are connected to the same NAT-type virtual network, named default, which uses the virbr0 interface. For details, see Section 13.1.2, “Virtual networking default configuration”.

For basic outbound-only network access from VMs, no additional network setup is usually needed, because the default network is installed along with the libvirt package, and is automatically started when the libvirtd service is started.

If a different VM network functionality is needed, you can create additional virtual networks and network interfaces and configure your VMs to use them. In addition to the default NAT, these networks and interfaces can be configured to use one of the following modes:

13.1.2. Virtual networking default configuration

When the libvirtd service is first installed on a virtualization host, it contains an initial virtual network configuration in network address translation (NAT) mode. By default, all VMs on the host are connected to the same libvirt virtual network, named default. VMs on this network can connect to locations both on the host and on the network beyond the host, but with the following limitations:

  • VMs on the network are visible to the host and other VMs on the host, but the network traffic is affected by the firewalls in the guest operating system’s network stack and by the libvirt network filtering rules attached to the guest interface.
  • VMs on the network can connect are not visible to locations outside the host. Outbound traffic is affected by the NAT rules, as well as the host system’s firewall.

The following diagram illustrates the default VM network configuration:

vn 08 network overview

13.2. Using the web console for managing virtual machine network interfaces

Using the RHEL 8 web console, you can manage the virtual network interfaces for the virtual machines to which the web console is connected. You can:

13.2.1. Viewing and editing virtual network interface information in the web console

Using the RHEL 8 web console, you can view and modify the virtual network interfaces on a selected virtual machine (VM):

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose information you want to see.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Network Interfaces.

    The Networks Interfaces pane appears with information about the virtual network interface configured for the VM.

    cockpit vNIC info

    The information includes the following:

    • Type - The type of network interface for the VM. Types include virtual network, bridge to LAN, and direct attachment.

      Note

      Generic Ethernet connection is not supported in RHEL 8.2.

    • Model type - The model of the virtual network interface.
    • MAC Address - The MAC address of the virtual network interface.
    • IP Address - The IP address of the virtual network interface.
    • Source - The source of the network interface. This is dependent on the network type.
    • State - The state of the virtual network interface.

  3. To edit the virtual network interface settings, Click Edit. The Virtual Network Interface Settings dialog opens.

    web console virtual network if settings
  4. Change the interface type, source, or model.

  5. Click Save. The network interface is modified.

    Note

    Changes to the virtual network interface settings take effect only after restarting the VM.

Additional resources

13.2.2. Connecting virtual network interfaces in the web console

Using the RHEL 8 web console, you can reconnect disconnected virtual network interface configured for a selected virtual machine (VM).

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose virtual network interface you want to connect.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down the VM.

  2. Click Network Interfaces.

    The Network Interfaces pane appears with information about the virtual network interfaces configured for the VM.

    cockpit vNIC plug

  3. Click Plug in the row of the virtual network interface you want to connect.

    The selected virtual network interface connects to the VM.

13.2.3. Disconnecting virtual network interfaces in the web console

Using the RHEL 8 web console, you can disconnect the virtual network interfaces connected to a selected virtual machine (VM).

Prerequisites

Procedure

  1. In the Virtual Machines interface, click the row of the VM whose virtual network interface you want to disconnect.

    The row expands to reveal the Overview pane with basic information about the selected VM and controls for shutting down and deleting the VM.

  2. Click Network Interfaces.

    The Network Interfaces pane appears with information about the virtual network interfaces configured for the VM.

    cockpit vNIC disconnect

  3. Click Unplug in the row of the virtual network interface you want to disconnect.

    The selected virtual network interface disconnects from the VM.

13.5. Types of virtual machine network connections

To modify the networking properties and behavior of your VMs, change the type of virtual network or interface the VMs use. The following sections describe the connection types available to VMs in RHEL 8.

13.5.1. Virtual networking with network address translation

By default, virtual network switches operate in network address translation (NAT) mode. They use IP masquerading rather than Source-NAT (SNAT) or Destination-NAT (DNAT). IP masquerading enables connected VMs to use the host machine’s IP address for communication with any external network. When the virtual network switch is operating in NAT mode, computers external to the host cannot communicate with the VMs inside the host.

vn 04 hostwithnatswitch
Warning

Virtual network switches use NAT configured by iptables rules. Editing these rules while the switch is running is not recommended, because incorrect rules may result in the switch being unable to communicate.

13.5.2. Virtual networking in routed mode

When using Routed mode, the virtual switch connects to the physical LAN connected to the host machine, passing traffic back and forth without the use of NAT. The virtual switch can examine all traffic and use the information contained within the network packets to make routing decisions. When using this mode, the virtual machines (VMs) are all in a single subnet, separate from the host machine. The VM subnet is routed through a virtual switch, which exists on the host machine. This enables incoming connections, but requires extra routing-table entries for systems on the external network.

Routed mode uses routing based on the IP address:

vn 06 routed switch

Common topologies that use routed mode include DMZs and virtual server hosting.

DMZ

You can create a network where one or more nodes are placed in a controlled sub-network for security reasons. Such a sub-network is known as a demilitarized zone (DMZ).

vn 09 routed mode DMZ

Host machines in a DMZ typically provide services to WAN (external) host machines as well as LAN (internal) host machines. Since this requires them to be accessible from multiple locations, and considering that these locations are controlled and operated in different ways based on their security and trust level, routed mode is the best configuration for this environment.

Virtual server hosting

A virtual server hosting provider may have several host machines, each with two physical network connections. One interface is used for management and accounting, the other for the VMs to connect through. Each VM has its own public IP address, but the host machines use private IP addresses so that only internal administrators can manage the VMs.

vn 10 routed mode datacenter

13.5.3. Virtual networking in bridged mode

In most VM networking modes, VMs automatically create and connect to the virbr0 virtual bridge. In contrast, in bridged mode, the VM connects to an existing Linux bridge on the host. As a result, the VM is directly visible on the physical network. This enables incoming connections, but does not require any extra routing-table entries.

Bridged mode uses connection switching based on the MAC address:

vn Bridged Mode Diagram

In bridged mode, the VM appear within the same subnet as the host machine. All other physical machines on the same physical network can detect the VM and access it.

Bridged network bonding

It is possible to use multiple physical bridge interfaces on the hypervisor by joining them together with a bond. The bond can then be added to a bridge, after which the VMs can be added to the bridge as well. However, the bonding driver has several modes of operation, and not all of these modes work with a bridge where VMs are in use.

The following bonding modes are usable:

  • mode 1
  • mode 2
  • mode 4

In contrast, using modes 0, 3, 5, or 6 is likely to cause the connection to fail. Also note that media-independent interface (MII) monitoring should be used to monitor bonding modes, as Address Resolution Protocol (ARP) monitoring does not work correctly.

For more information on bonding modes, refer to the Red Hat Knowledgebase.

Common scenarios

The most common use cases for bridged mode include:

  • Deploying VMs in an existing network alongside host machines, making the difference between virtual and physical machines invisible to the end user.
  • Deploying VMs without making any changes to existing physical network configuration settings.
  • Deploying VMs that must be easily accessible to an existing physical network. Placing VMs on a physical network where they must access DHCP services.
  • Connecting VMs to an existing network where virtual LANs (VLANs) are used.

Additional resources

13.5.4. Virtual networking in isolated mode

When using isolated mode, virtual machines connected to the virtual switch can communicate with each other and with the host machine, but their traffic will not pass outside of the host machine, and they cannot receive traffic from outside the host machine. Using dnsmasq in this mode is required for basic functionality such as DHCP.

vn 07 isolated switch

13.5.5. Virtual networking in open mode

When using open mode for networking, libvirt does not generate any iptables rules for the network. As a result, libvirt does not overwrite iptables rules provided by the host, and the user can therefore manually manage the VM’s iptables rules.

13.5.6. Direct attachment of the virtual network device

You can use the macvtap driver to attach a virtual machine’s NIC directly to a specified physical interface of the host machine. The macvtap connection has a number of modes, including private mode.

In this mode, all packets are sent to the external switch and will only be delivered to a target VM on the same host machine if they are sent through an external router or gateway and these send them back to the host. Private mode can be used to prevent the individual VMs on a single host from communicating with each other.

virt macvtap modes private

Additional resources

13.5.7. Comparison of virtual machine connection types

The following table provides information about the locations to which selected types of virtual machine (VM) network configurations can connect, and to which they are visible.

Table 13.1. Virtual machine connection types

 Connection to the hostConnection to other VMs on the hostConnection to outside locationsVisible to outside locations

Bridged mode

YES

YES

YES

YES

NAT

YES

YES

YES

no

Routed mode

YES

YES

YES

YES

Isolated mode

YES

YES

no

no

Private mode

no

no

YES

YES

Open mode

Depends on the host’s iptables rules

13.6. Additional resources

Chapter 14. Sharing files between the host and its virtual machines

You may frequently require to share data between your host system and the virtual machines (VMs) it runs. To do so quickly and efficiently, you can set up NFS or Samba file shares on your system.

14.1. Sharing files between the host and Linux virtual machines

For efficient file sharing between your host system and the Linux VMs it is connected to, you can export an NFS share that your VMs can mount and access.

Prerequisites

  • The nfs-utils package is installed on the host.

  • A directory that you want to share with your VMs. If you do not want to share any of your existing directories, create a new one, for example named shared-files. 

    # mkdir shared-files

  • The host is visible and reachable over a network for the VM. This is generally the case if the VM is connected using the NAT and bridge type of virtual networks. However, for the macvtap connection, you must first set up the macvlan feature on the host. To do so:

    1. Create a network device file in the host’s /etc/systemd/network/ directory, for example called vm-macvlan.netdev. 

      # vim /etc/systemd/network/vm-macvlan.netdev

    2. Edit the network device file to have the following content. You can replace vm-macvlan with the name you chose for your network device. 

      [NetDev]
Name=vm-macvlan
Kind=macvlan

[MACVLAN]
Mode=bridge

    3. Create a network configuration file for your macvlan network device, for example vm-macvlan.network. 

      # vim /etc/systemd/network/vm-macvlan.network

    4. Edit the network configuration file to have the following content. You can replace vm-macvlan with the name you chose for your network device. 

      [Match]
Name=_vm-macvlan_

[Network]
IPForward=yes
Address=192.168.250.33/24
Gateway=192.168.250.1
DNS=192.168.250.1

    5. Create a network configuration file for your physical network interface. For example, if your interface is enp4s0: 

      # vim /etc/systemd/network/enp4s0.network

      If you are unsure what interface name to use, you can use the ifconfig command on your host to obtain the list of active network interfaces.

    6. Edit the physical network configuration file to make the physical network a part of the macvlan interface, in this case vm-macvlan: 

      [Match]
Name=enp4s0

[Network]
MACVLAN=vm-macvlan
    7. Reboot your host.
  • Optional: For improved security, ensure your VMs are compatible with NFS version 4 or later.

Procedure

  1. On the host, export a directory with the files you want to share as a network file system (NFS).

    1. Obtain the IP address of each virtual machine you want to share files with. The following example obtains the IPs of testguest1 and testguest2. 

      # virsh domifaddr testguest1
Name       MAC address          Protocol     Address
----------------------------------------------------------------
vnet0      52:53:00:84:57:90    ipv4         192.168.124.220/24

# virsh domifaddr testguest2
Name       MAC address          Protocol     Address
----------------------------------------------------------------
vnet1      52:53:00:65:29:21    ipv4         192.168.124.17/24

    2. Edit the /etc/exports file on the host and add a line that includes the directory you want to share, IPs of VMs you want to share with, and sharing options. 

      Shared directory VM1-IP(options) VM2-IP(options) [...]

      For example, the following shares the /usr/local/shared-files directory on the host with testguest1 and testguest2, and enables the VMs to edit the content of the directory: 

      /usr/local/shared-files/ 192.168.124.220(rw,sync) 192.168.124.17(rw,sync)

    3. Export the updated file system. 

      # exportfs -a

    4. Ensure the NFS process is started: 

      # systemctl start nfs-server

    5. Obtain the IP address of the host system. This will be used for mounting the shared directory on the VMs later. 

      # ip addr
[...]
5: virbr0: [BROADCAST,MULTICAST,UP,LOWER_UP] mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 52:54:00:32:ff:a5 brd ff:ff:ff:ff:ff:ff
    inet 192.168.124.1/24 brd 192.168.124.255 scope global virbr0
       valid_lft forever preferred_lft forever
[...]

      Note that the relevant network is the one being used use for connection to the host by the VMs you want to share files with. Usually, this is virbr0.

  2. On the guest OS of a VM specified in the /etc/exports file, mount the exported file system.

    1. Create a directory you want to use as a mount point for the shared file system, for example /mnt/host-share: 

      # mkdir /mnt/host-share

    2. Mount the directory exported by the host on the mount point. This example mounts the /usr/local/shared-files directory exported by the 192.168.124.1 host on /mnt/host-share in the guest: 

      # mount 192.168.124.1:/usr/local/shared-files /mnt/host-share

    3. To verify the mount has succeeded, access and explore the shared directory on the mount point: 

      # cd /mnt/host-share
# ls
shared-file1  shared-file2  shared-file3

14.2. Sharing files between the host and Windows virtual machines

For efficient file sharing between your host system and the Windows VMs it is connected to, you can prepare a Samba server that your VMs can access.

Prerequisites

  • The samba packages are installed on your host. If they are not: 

    # yum install samba

  • The host is visible and reachable over a network for the VM. This is generally the case if the VM is connected using the NAT and bridge type of virtual networks. However, for the macvtap connection, you must first set up the macvlan feature on the host. To do so:

    1. Create a network device file, for example called vm-macvlan.netdev in the host’s /etc/systemd/network/ directory. 

      # vim /etc/systemd/network/vm-macvlan.netdev

    2. Edit the network device file to have the following content. You can replace vm-macvlan with the name you chose for your network device. 

      [NetDev]
Name=vm-macvlan
Kind=macvlan

[MACVLAN]
Mode=bridge

    3. Create a network configuration file for your macvlan network device, for example vm-macvlan.network. 

      # vim /etc/systemd/network/vm-macvlan.network

    4. Edit the network configuration file to have the following content. You can replace vm-macvlan with the name you chose for your network device. 

      [Match]
Name=_vm-macvlan_

[Network]
IPForward=yes
Address=192.168.250.33/24
Gateway=192.168.250.1
DNS=192.168.250.1

    5. Create a network configuration file for your physical network interface. For example, if your interface is enp4s0: 

      # vim /etc/systemd/network/enp4s0.network

      If you are unsure what interface to use, you can use the ifconfig command on your host to obtain the list of active network interfaces.

    6. Edit the physical network configuration file to make the physical network a part of the macvlan interface, in this case vm-macvlan: 

      [Match]
Name=enp4s0

[Network]
MACVLAN=vm-macvlan
    7. Reboot your host.

Procedure

  1. On the host, create a Samba share and make it accessible for external systems.

    1. Add firewall permissions for Samba. 

      # firewall-cmd --permanent --zone=public --add-service=samba
success
# firewall-cmd --reload
success

    2. Edit the /etc/samba/smb.conf file:

      1. Add the following to the [global] section: 

        map to guest = Bad User

      2. Add the following at the end of the file: 

        #=== Share Definitions ===
[VM-share]
path = /samba/VM-share
browsable = yes
guest ok = yes
read only = no
hosts allow = 192.168.122.0/24

        Note that the hosts allow line restricts the accessibility of the share only to hosts on the VM network. If you want the share to be accessible by anyone, remove the line.

    3. Create the /samba/VM-share directory. 

      # mkdir -p /samba/VM-share

    4. Enable the Samba service. 

      # systemctl enable smb.service
Created symlink /etc/systemd/system/multi-user.target.wants/smb.service → /usr/lib/systemd/system/smb.service.

    5. Restart the Samba service. 

      # systemctl restart smb.service

    6. Allow the VM-share directory to be accessible and modifiable for the VMs. 

      # chmod -R 0755 /samba/VM-share/
# chown -R nobody:nobody /samba/VM-share/

    7. Add the SELinux Samba sharing label to /etc/samba/VM-share/ 

      # chcon -t samba_share_t /samba/VM-share/

  2. On the Windows guest operating system, attach the Samba share as a network location.

    1. Open the File Explorer and right-click "This PC".

    2. In the context menu, click Add a network location.

      virt Win10 network loc1
    3. In the Add Network Location wizard that opens, select "Choose a custom network location" and click Next.

    4. In the "Internet or network address" field, type host-IP/VM-share, where host-IP is the IP address of the host. Usually, the host IP is the default gateway of the VM. Afterwards, click Next.

      virt Win10 network loc2
    5. When the wizard asks if you want to rename the shared directory, keep the default name. This ensures the consistency of file sharing configuration across the VM and the guest. Click Next.
    6. If accessing the network location was successful, you can now click Finish and open the shared directory.

Chapter 15. Securing virtual machines

As an administrator of a RHEL 8 system with virtual machines (VMs), ensuring that your VMs are as secure as possible significantly lowers the risk of your guest and host OSs being infected by malicious software.

This document outlines the mechanics of securing VMs on a RHEL 8 host and provides a list of methods to increase the security of your VMs.

15.1. How security works in virtual machines

When using virtual machines (VMs), multiple operating systems can be housed within a single host machine. These systems are connected with the host through the hypervisor, and usually also through a virtual network. As a consequence, each VM can be used as a vector for attacking the host with malicious software, and the host can be used as a vector for attacking any of the VMs.

Figure 15.1. A potential malware attack vector on a virtualization host

virt sec successful attack

Because the hypervisor uses the host kernel to manage VMs, services running on the VM’s operating system are frequently used for injecting malicious code into the host system. However, you can protect your system against such security threats by using a number of security features on your host and your guest systems.

These features, such as SELinux or QEMU sandboxing, provide various measures that make it more difficult for malicious code to attack the hypervisor and transfer between your host and your VMs.

Figure 15.2. Prevented malware attacks on a virtualization host

virt sec prevented attack

Many of the features that RHEL 8 provides for VM security are always active and do not have to be enabled or configured. For details, see Section 15.4, “Automatic features for virtual machine security”.

In addition, you can adhere to a variety of best practices to minimize the vulnerability of your VMs and your hypervisor. For more information, see Section 15.2, “Best practices for securing virtual machines”.

15.2. Best practices for securing virtual machines

Following the instructions below significantly decreases the risk of your virtual machines being infected with malicious code and used as attack vectors to infect your host system.

On the guest side:

  • Secure the virtual machine as if it was a physical machine. The specific methods available to enhance security depend on the guest OS.

    If your VM is running RHEL 8, see Configuring and managing security in RHEL 8 for detailed instructions on improving the security of your guest system.

On the host side:

  • When managing VMs remotely, use cryptographic utilities such as SSH and network protocols such as SSL for connecting to the VMs.

  • Ensure SELinux is in Enforcing mode: 

    # getenforce
Enforcing

    If SELinux is disabled or in Permissive mode, see the Using SELinux document for instructions on activating Enforcing mode.

    Note

    SELinux Enforcing mode also enables the sVirt RHEL 8 feature. This is a set of specialized SELinux booleans for virtualization, which can be manually adjusted for fine-grained VM security management.

  • Use VMs with SecureBoot:

    SecureBoot is a feature that ensures that your VM is running a cryptographically signed OS. This prevents VMs whose OS has been altered by a malware attack from booting.

    SecureBoot can only be applied when installing a Linux VM that uses OVMF firmware. For instructions, see Section 15.3, “Creating a SecureBoot virtual machine”.

  • Do not use qemu-* commands, such as qemu-img.

    QEMU is an essential component of the virtualization architecture in RHEL 8, but it is difficult to manage manually, and improper QEMU configurations may cause security vulnerabilities. Therefore, using qemu-* commands is not supported by Red Hat. Instead, it is highly recommended to interact with QEMU using libvirt utilities, such as virsh, virt-install, and virt-xml, as these orchestrate QEMU according to the best practices.

Additional resources

15.3. Creating a SecureBoot virtual machine

The following provides instructions on creating a Linux virtual machine (VM) that uses the SecureBoot feature, which ensures that your VM is running a cryptographically signed OS. If the guest OS of a VM has been altered by malware, SecureBoot prevents the VM from booting, which stops the potential spread of the malware to your host machine.

Prerequisites

  • The VM is using the Q35 machine type.

  • The edk2-OVMF packages is installed: 

    # yum install edk2-ovmf

  • An operating system (OS) installation source is available locally or on a network. This can be one of the following formats:

    • An ISO image of an installation medium
    • A disk image of an existing VM installation
  • Optional: A Kickstart file can be provided for faster and easier configuration of the installation.

Procedure

  1. Use the virt-install command to create a VM as detailed in Section 2.2.1, “Creating virtual machines using the command-line interface”. For the --boot option, use the uefi,nvram_template=/usr/share/OVMF/OVMF_VARS.secboot.fd value. This uses the OVMF_VARS.secboot.fd and OVMF_CODE.secboot.fd files as templates for the VM’s non-volatile RAM (NVRAM) settings, which enables the SecureBoot feature.

    For example: 

    # virt-install --name rhel8sb --memory 4096 --vcpus 4 --os-variant rhel8.0 --boot uefi,nvram_template=/usr/share/OVMF/OVMF_VARS.secboot.fd --disk boot_order=2,size=10 --disk boot_order=1,device=cdrom,bus=scsi,path=/images/RHEL-8.0-installation.iso
  2. Follow the OS installation procedure according to the instructions on the screen.

Verification

  1. After the guest OS is installed, access the VM’s command line by opening the terminal in the graphical guest console or connecting to the guest OS using SSH.

  2. To confirm that SecureBoot has been enabled on the VM, use the mokutil --sb-state command: 

    # mokutil --sb-state
SecureBoot enabled

Additional resources

15.4. Automatic features for virtual machine security

In addition to manual means of improving the security of your virtual machines listed in Section 15.2, “Best practices for securing virtual machines”, a number of security features are provided by the libvirt software suite and are automatically enabled when using virtualization in RHEL 8. These include:

System and user sessions

To access all the available utilities for virtual machine management in RHEL 8, you need to use the system session of libvirt. To do so, you must have root privileges on the system or be a part of the libvirt user group.

Non-root users that are not in the libvirt group can only access a user session of libvirt, which has to respect the access rights of the local user when accessing resources. For example, in the user session, you cannot detect or access VMs created in the system session or by other users. Also, available VM networking configuration options are significantly limited.

Note

The RHEL 8 documentation assumes you have libvirt system session privileges.

Virtual machine separation
Individual VMs run as isolated processes on the host, and rely on security enforced by the host kernel. Therefore, a VM cannot read or access the memory or storage of other VMs on the same host.
QEMU sandboxing
A feature that prevents QEMU code from executing system calls that can compromise the security of the host.
Kernel Address Space Randomization (KASLR)
Enables randomizing the physical and virtual addresses at which the kernel image is decompressed. Thus, KASLR prevents guest security exploits based on the location of kernel objects.

15.5. Virtualization booleans

For fine-grained configuration of virtual machines security on a RHEL 8 system, you can configure SELinux booleans on the host to ensure the hypervisor acts in a specific way.

To list all virtualization-related booleans and their statuses, use the getsebool -a | grep virt command: 

$ getsebool -a | grep virt
[...]
virt_sandbox_use_netlink --> off
virt_sandbox_use_sys_admin --> off
virt_transition_userdomain --> off
virt_use_comm --> off
virt_use_execmem --> off
virt_use_fusefs --> off
[...]

To enable a specific boolean, use the setsebool -P boolean_name on command as root. To disable a boolean, use setsebool -P boolean_name off.

The following table lists virtualization-related booleans available in RHEL 8 and what they do when enabled:

Table 15.1. SELinux virtualization booleans

SELinux BooleanDescription

staff_use_svirt

Enables non-root users to create and transition VMs to sVirt.

unprivuser_use_svirt

Enables unprivileged users to create and transition VMs to sVirt.

virt_sandbox_use_audit

Enables sandbox containers to send audit messages.

virt_sandbox_use_netlink

Enables sandbox containers to use netlink system calls.

virt_sandbox_use_sys_admin

Enables sandbox containers to use sys_admin system calls, such as mount.

virt_transition_userdomain

Enables virtual processes to run as user domains.

virt_use_comm

Enables virt to use serial/parallel communication ports.

virt_use_execmem

Enables confined virtual guests to use executable memory and executable stack.

virt_use_fusefs

Enables virt to read FUSE mounted files.

virt_use_nfs

Enables virt to manage NFS mounted files.

virt_use_rawip

Enables virt to interact with rawip sockets.

virt_use_samba

Enables virt to manage CIFS mounted files.

virt_use_sanlock

Enables confined virtual guests to interact with the sanlock.

virt_use_usb

Enables virt to use USB devices.

virt_use_xserver

Enables virtual machine to interact with the X Window System.

15.6. Setting up IBM Secure Execution on IBM Z

When using IBM Z hardware to run a RHEL 8 host, you can improve the security of your virtual machines (VMs) by configuring IBM Secure Execution for the VMs.

IBM Secure Execution, also known as Protected Virtualization, prevents the host system from accessing a VM’s state and memory contents. As a result, even if the host is compromised, it cannot be used as a vector for attacking the guest operating system. In addition, Secure Execution can be used to prevent untrusted hosts from obtaining sensitive information from the VM.

The following procedure describes how to convert an existing VM on an IBM Z host into a secured VM.

Prerequisites

  • The system hardware is one of the following:

    • IBM z15 or later
    • IBM LinuxONE III or later

  • The Secure Execution feature is enabled for your system. To verify, use: 

    # grep facilities /proc/cpuinfo | grep 158

    If this command displays any output, your CPU is compatible with Secure Execution.

  • The kernel includes support for Secure Execution. To confirm, use: 

    # ls /sys/firmware | grep uv

    If the command generates any output, your kernel supports Secure Execution.

  • The host CPU model contains the unpack facility. To confirm, use: 

    # virsh domcapabilities | grep unpack
<feature policy='require' name='unpack'/>

    If the command generates the above output, your CPU host model is compatible with Secure Execution.

  • The CPU mode of the VM is set to host-model. To confirm this, use the following and replace vm-name with the name of your VM. 

    # virsh dumpxml vm-name | grep "<cpu mode='host-model'/>"

    If the command generates any output, the VM’s CPU mode is set correctly.

Procedure

  1. Add the prot_virt=1 kernel parameter to the boot configuration of the host. 

    # # grubby --update-kernel=ALL --args="prot_virt=1"

  2. Create a parameter file for the VM you want to secure. For example: 

    # touch ~/secure-parameters

  3. In the /boot/loader/entries directory of the host, identify the boot loader entry with the latest version: 

    # ls /boot/loader/entries -l
[...]
-rw-r--r--. 1 root root  281 Oct  9 15:51 3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf

  4. Retrieve the kernel options line of the boot loader entry: 

    # cat /boot/loader/entries/3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf | grep options
options root=/dev/mapper/rhel-root crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap

  5. Add the content of the options line and swiotlb=262144 to the created parameters file. 

    # echo "root=/dev/mapper/rhel-root crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap swiotlb=262144" > ~/secure-parameters

  6. Generate an IBM Secure Execution image for the selected VM.

    For example, the following creates a /boot/secure-image secured image based on the /boot/vmlinuz-4.18.0-240.el8.s390x image, using the secure-parameters file, the /boot/initramfs-4.18.0-240.el8.s390x.img initial RAM disk file, and the HKD-8651-000201C048.crt host key document. 

    # genprotimg -i /boot/vmlinuz-4.18.0-240.el8.s390x -r /boot/initramfs-4.18.0-240.el8.s390x.img -p ~/secure-parameters -k HKD-8651-00020089A8.crt -o /boot/secure-image

    Using the genprotimg utility creates the secure image, which contains the kernel parameters, initial RAM disk, and boot image.

  7. In the guest operating system of the VM, update the VM’s boot menu to boot from the secure image. In addition, remove the lines starting with initrd and options, as they are not needed.

    For example, in a RHEL 8.3 VM, the boot menu can be edited in the /boot/loader/entries/ directory: 

    # cat /boot/loader/entries/3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf
title Red Hat Enterprise Linux 8.3
version 4.18.0-240.el8.s390x
linux /boot/secure-image
[...]

  8. Enable virtio devices to use shared buffers. To do so, use virsh edit to modify the XML configuration of the VM, and add iommu='on' to the <driver> line of all devices that have one. For example: 

    <interface type='network'>
  <source network='default'/>
  <model type='virtio'/>
  <driver name='vhost' iommu='on'/>
</interface>

    If a device configuration does not contain any <driver> line, add <driver iommu='on'\> instead.

  9. Disable memory ballooning on the VM, as the feature is not compatible with Secure Execution. To do so, add the following line to the VM’s XML configuration. 

    <memballoon model='none'/>

  10. Create the bootable disk image 

    # zipl -V

  11. Securely remove the original unprotected files. For example: 

    # shred /boot/vmlinuz-4.18.0-240.el8.s390x
# shred /boot/initramfs-4.18.0-240.el8.s390x.img
# shred secure-parameters

    The original boot image, the initial RAM image, and the kernel parameter file are unprotected, and if they are not removed, VMs with Secure Execution enabled can still be vulnerable to hacking attempts or sensitive data mining.

Verification

  • On the host, use the virsh dumpxml utility to confirm the XML configuration of the secured VM. The configuration must include the <driver iommu='on'/> and <memballoon model='none'/> elements. 

    # virsh dumpxml vm-name
[...]
  <cpu mode='host-model'/>
  <devices>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none' io='native' iommu='on'>
      <source file='/var/lib/libvirt/images/secure-guest.qcow2'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <interface type='network'>
      <driver iommu='on'/>
      <source network='default'/>
      <model type='virtio'/>
    </interface>
    <console type='pty'/>
    <memballoon model='none'/>
  </devices>
</domain>

Additional resources

15.7. Attaching cryptographic coprocessors to virtual machines on IBM Z

To use hardware encryption in your virtual machine (VM) on an IBM Z host, create mediated devices from a cryptographic coprocessor device and assign them to the intended VMs. For detailed instructions, see below.

Prerequisites

  • Your host is running on IBM Z hardware.

  • The cryptographic coprocessor is compatible with device assignment. To confirm this, ensure that the type of your coprocessor is listed as CEX4 or later. 

    # lszcrypt -V

CARD.DOMAIN TYPE  MODE        STATUS  REQUESTS  PENDING HWTYPE QDEPTH FUNCTIONS  DRIVER
--------------------------------------------------------------------------------------------
05         CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4card
05.0004    CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
05.00ab    CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
  • The mdevctl package is installed.

  • The vfio_ap kernel module is loaded. To verify, use: 

    # lsmod | grep vfio_ap
vfio_ap         24576  0
[...]

    To load the module, use: 

    # modprobe vfio_ap

Procedure

  1. On the host, reassign your crypto device to the vfio-ap drivers. The following example assigns two crypto devices with bitmask IDs (0x05, 0x0004) and (0x05, 0x00ab) to vfio-ap. 

    #  echo -0x05 > /sys/bus/ap/apmask
#  echo -0x0004, -0x00ab > /sys/bus/ap/aqmask

    For information on identifying the bitmask ID values, see Preparing pass-through devices for cryptographic adapter resources in the KVM Virtual Server Management document from IBM.

  2. Verify that the crypto devices have been reassigned correctly. 

    # lszcrypt -V

CARD.DOMAIN TYPE  MODE        STATUS  REQUESTS  PENDING HWTYPE QDEPTH FUNCTIONS  DRIVER
--------------------------------------------------------------------------------------------
05          CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  cex4card
05.0004     CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  vfio_ap
05.00ab     CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  vfio_ap

    If the DRIVER values of the domain queues changed to vfio_ap, the reassignment succeeded.

  3. Generate a device UUID. 

    # uuidgen
669d9b23-fe1b-4ecb-be08-a2fabca99b71

    In the following steps of this procedure, replace 669d9b23-fe1b-4ecb-be08-a2fabca99b71 with your generated UUID.

  4. Using the UUID, create a new vfio_ap device.

    The following example shows creating a persistent mediated device and assigning queues to it. For example, the following commands assign domain adapter 0x05 and domain queues 0x0004 and 0x00ab to device 669d9b23-fe1b-4ecb-be08-a2fabca99b71. 

    # mdevctl define --uuid 669d9b23-fe1b-4ecb-be08-a2fabca99b71 --parent matrix --type vfio_ap-passthrough
# mdevctl modify --uuid 669d9b23-fe1b-4ecb-be08-a2fabca99b71 --addattr=assign_adapter --value=0x05
# mdevctl modify --uuid 669d9b23-fe1b-4ecb-be08-a2fabca99b71 --addattr=assign_domain --value=0x0004
# mdevctl modify --uuid 669d9b23-fe1b-4ecb-be08-a2fabca99b71 --addattr=assign_domain --value=0x00ab

  5. Start the mediated device. 

    # mdevctl start --uuid 669d9b23-fe1b-4ecb-be08-a2fabca99b71

  6. Check that the configuration has been applied correctly 

    # cat /sys/devices/vfio_ap/matrix/mdev_supported_types/vfio_ap-passthrough/devices/669d9b23-fe1b-4ecb-be08-a2fabca99b71
05.0004
05.00ab

    If the output contains the numerical values of queues that you have previously assigned to vfio-ap, the process was successful.

  7. Use the virsh edit command to open the XML configuration of the VM where you want to use the crypto devices. 

    # virsh edit vm-name

  8. Add the following lines to the <devices> section in the XML configuration, and save it. 

    <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-ap'>
  <source>
    <address uuid='669d9b23-fe1b-4ecb-be08-a2fabca99b71'/>
  </source>
</hostdev>

    Note that each UUID can only be assigned to one VM at a time.

Verification

  1. Start the VM to which you assigned the mediated device.

  2. After the guest operating system (OS) boots, ensure that it detects the assigned crypto devices. 

    # lszcrypt -V

CARD.DOMAIN TYPE  MODE        STATUS  REQUESTS  PENDING HWTYPE QDEPTH FUNCTIONS  DRIVER
--------------------------------------------------------------------------------------------
05          CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4card
05.0004     CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
05.00ab     CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue

    The output of this command in the guest OS will be identical to that on a host logical partition with the same cryptographic coprocessor devices available.

15.8. Enabling standard hardware security on Windows virtual machines

To secure Windows virtual machines (VMs), you can enable basic level security using the standard hardware capabilities of the Windows device.

Prerequisites

  • Make sure you have installed the latest WHQL certified VirtIO drivers.
  • Make sure the VM’s firmware supports UEFI boot.

  • Install the edk2-OVMF package on your host machine. 

    # yum install edk2-ovmf

  • Install the vTPM packages on your host machine. 

    # yum install swtpm libtpms
  • Make sure the VM is using the Q35 machine architecture.
  • Make sure you have the Windows installation media.

Procedure

  1. Enable TPM 2.0 by adding the following parameters to the <devices> section in the VM’s XML configuration. 

    <devices>
[...]
  <tpm model='tpm-crb'>
    <backend type='emulator' version='2.0'/>
  </tpm>
[...]
</devices>
  2. Install Windows in UEFI mode. For more information on how to do so, see Creating a SecureBoot virtual machine.
  3. Install the VirtIO drivers on the Windows VM. For more information on how to do so, see Installing virtio drivers on a Windows guest.
  4. In UEFI, enable Secure Boot. For more information on how to do so, see Secure Boot.

Verification

  • Ensure that the Device Security page on your Windows machine displays the following message: 

    Your device meets the requirements for standard hardware security.

Chapter 16. Optimizing virtual machine performance

Virtual machines (VMs) always experience some degree of performance deterioration in comparison to the host. The following sections explain the reasons for this deterioration and provide instructions on how to minimize the performance impact of virtualization in RHEL 8, so that your hardware infrastructure resources can be used as efficiently as possible.

16.1. What influences virtual machine performance

VMs are run as user-space processes on the host. The hypervisor therefore needs to convert the host’s system resources so that the VMs can use them. As a consequence, a portion of the resources is consumed by the conversion, and the VM therefore cannot achieve the same performance efficiency as the host.

The impact of virtualization on system performance

More specific reasons for VM performance loss include:

  • Virtual CPUs (vCPUs) are implemented as threads on the host, handled by the Linux scheduler.
  • VMs do not automatically inherit optimization features, such as NUMA or huge pages, from the host kernel.
  • Disk and network I/O settings of the host might have a significant performance impact on the VM.
  • Network traffic typically travels to a VM through a software-based bridge.
  • Depending on the host devices and their models, there might be significant overhead due to emulation of particular hardware.

The severity of the virtualization impact on the VM performance is influenced by a variety factors, which include:

  • The number of concurrently running VMs.
  • The amount of virtual devices used by each VM.
  • The device types used by the VMs.

Reducing VM performance loss

RHEL 8 provides a number of features you can use to reduce the negative performance effects of virtualization. Notably:

Important

Tuning VM performance can have adverse effects on other virtualization functions. For example, it can make migrating the modified VM more difficult.

16.2. Optimizing virtual machine performance using tuned

The tuned utility is a tuning profile delivery mechanism that adapts RHEL for certain workload characteristics, such as requirements for CPU-intensive tasks or storage-network throughput responsiveness. It provides a number of tuning profiles that are pre-configured to enhance performance and reduce power consumption in a number of specific use cases. You can edit these profiles or create new profiles to create performance solutions tailored to your environment, including virtualized environments.

Red Hat recommends using the following profiles when using virtualization in RHEL 8:

  • For RHEL 8 virtual machines, use the virtual-guest profile. It is based on the generally applicable throughput-performance profile, but also decreases the swappiness of virtual memory.
  • For RHEL 8 virtualization hosts, use the virtual-host profile. This enables more aggressive writeback of dirty memory pages, which benefits the host performance.

Prerequisites

Procedure

To enable a specific tuned profile:

  1. List the available tuned profiles. 

    # tuned-adm list

Available profiles:
- balanced             - General non-specialized tuned profile
- desktop              - Optimize for the desktop use-case
[...]
- virtual-guest        - Optimize for running inside a virtual guest
- virtual-host         - Optimize for running KVM guests
Current active profile: balanced

  2. Optional: Create a new tuned profile or edit an existing tuned profile.

    For more information, see Customizing tuned profiles.

  3. Activate a tuned profile. 

    # tuned-adm profile selected-profile

    • To optimize a virtualization host, use the virtual-host profile. 

      # tuned-adm profile virtual-host

    • On a RHEL guest operating system, use the virtual-guest profile. 

      # tuned-adm profile virtual-guest

Additional resources

16.3. Configuring virtual machine memory

To improve the performance of a virtual machine (VM), you can assign additional host RAM to the VM. Similarly, you can decrease the amount of memory allocated to a VM so the host memory can be allocated to other VMs or tasks.

To perform these actions, you can use the web console or the command-line interface.

16.3.1. Adding and removing virtual machine memory using the web console

To improve the performance of a virtual machine (VM) or to free up the host resources it is using, you can use the web console to adjust amount of memory allocated to the VM.

Prerequisites

  • The guest OS is running the memory balloon drivers. To verify this is the case:

    1. Ensure the VM’s configuration includes the memballoon device: 

      # virsh dumpxml testguest | grep memballoon
<memballoon model='virtio'>
    </memballoon>

      If this commands displays any output and the model is not set to none, the memballoon device is present.

    2. Ensure the ballon drivers are running in the guest OS.

  • To use the web console to manage VMs, install the web console VM plug-in.

Procedure

  1. Optional: Obtain the information about the maximum memory and currently used memory for a VM. This will serve as a baseline for your changes, and also for verification. 

    # virsh dominfo testguest
Max memory:     2097152 KiB
Used memory:    2097152 KiB

  2. In the Virtual Machines interface, click a row with the name of the VMs for which you want to view and adjust the allocated memory.

    The row expands to reveal the Overview pane with basic information about the selected VMs.

  3. Click the value of the Memory line in the Overview pane.

    The Memory Adjustment dialog appears.

    virt memory cockpit

  4. Configure the virtual CPUs for the selected VM.

    • Maximum allocation - Sets the maximum amount of host memory that the VM can use for its processes. Increasing this value improves the performance potential of the VM, and reducing the value lowers the performance footprint the VM has on your host.

      Adjusting maximum memory allocation is only possible on a shut-off VM.

    • Current allocation - Sets the actual amount of memory allocated to the VM. You can adjust the value to regulate the memory available to the VM for its processes. This value cannot exceed the maximum allocation value.

  5. Click Save.

    The memory allocation of the VM is adjusted.

Additional resources

16.3.2. Adding and removing virtual machine memory using the command-line interface

To improve the performance of a virtual machine (VM) or to free up the host resources it is using, you can use the CLI to adjust amount of memory allocated to the VM.

Prerequisites

  • The guest OS is running the memory balloon drivers. To verify this is the case:

    1. Ensure the VM’s configuration includes the memballoon device: 

      # virsh dumpxml testguest | grep memballoon
<memballoon model='virtio'>
    </memballoon>

      If this commands displays any output and the model is not set to none, the memballoon device is present.

    2. Ensure the ballon drivers are running in the guest OS.

Procedure

  1. Optional: Obtain the information about the maximum memory and currently used memory for a VM. This will serve as a baseline for your changes, and also for verification. 

    # virsh dominfo testguest
Max memory:     2097152 KiB
Used memory:    2097152 KiB

  2. Adjust the maximum memory allocated to a VM. Increasing this value improves the performance potential of the VM, and reducing the value lowers the performance footprint the VM has on your host. Note that this change can only be performed on a shut-off VM, so adjusting a running VM requires a reboot to take effect.

    For example, to change the maximum memory that the testguest VM can use to 4096 MiB: 

    # virt-xml testguest --edit --memory memory=4096,currentMemory=4096
Domain 'testguest' defined successfully.
Changes will take effect after the domain is fully powered off.

  1. Optional: You can also adjust the memory currently used by the VM, up to the maximum allocation. This regulates the memory load that the VM has on the host until the next reboot, without changing the maximum VM allocation. 

    # virsh setmem testguest --current 2048

Verification

  1. Confirm that the memory used by the VM has been updated: 

    # virsh dominfo testguest
Max memory:     4194304 KiB
Used memory:    2097152 KiB

  2. Optional: If you adjusted the current VM memory, you can obtain the memory balloon statistics of the VM to evaluate how effectively it regulates its memory use. 

     # virsh domstats --balloon testguest
Domain: 'testguest'
  balloon.current=365624
  balloon.maximum=4194304
  balloon.swap_in=0
  balloon.swap_out=0
  balloon.major_fault=306
  balloon.minor_fault=156117
  balloon.unused=3834448
  balloon.available=4035008
  balloon.usable=3746340
  balloon.last-update=1587971682
  balloon.disk_caches=75444
  balloon.hugetlb_pgalloc=0
  balloon.hugetlb_pgfail=0
  balloon.rss=1005456

Additional resources

16.3.3. Additional resources

  • To increase the maximum memory of a running VM, you can attach a memory device to the VM. This is also referred to as memory hot plug. For details, see Section 10.2, “Attaching devices to virtual machines”.

    Note that removing a memory device from a VM, also known as memory hot unplug, is not supported in RHEL 8, and Red Hat highly discourages its use.

16.4. Optimizing virtual machine I/O performance

The input and output (I/O) capabilities of a virtual machine (VM) can significantly limit the VM’s overall efficiency. To address this, you can optimize a VM’s I/O by configuring block I/O parameters.

16.4.1. Tuning block I/O in virtual machines

When multiple block devices are being used by one or more VMs, it might be important to adjust the I/O priority of specific virtual devices by modifying their I/O weights.

Increasing the I/O weight of a device increases its priority for I/O bandwidth, and therefore provides it with more host resources. Similarly, reducing a device’s weight makes it consume less host resources.

Note

Each device’s weight value must be within the 100 to 1000 range. Alternatively, the value can be 0, which removes that device from per-device listings.

Procedure

To display and set a VM’s block I/O parameters:

  1. Display the current <blkio> parameters for a VM:

    # virsh dumpxml VM-name 

    <domain>
  [...]
  <blkiotune>
    <weight>800</weight>
    <device>
      <path>/dev/sda</path>
      <weight>1000</weight>
    </device>
    <device>
      <path>/dev/sdb</path>
      <weight>500</weight>
    </device>
  </blkiotune>
  [...]
</domain>

  2. Edit the I/O weight of a specified device: 

    # virsh blkiotune VM-name --device-weights device, I/O-weight

    For example, the following changes the weight of the /dev/sda device in the liftrul VM to 500. 

    # virsh blkiotune liftbrul --device-weights /dev/sda, 500

16.4.2. Disk I/O throttling in virtual machines

When several VMs are running simultaneously, they can interfere with system performance by using excessive disk I/O. Disk I/O throttling in KVM virtualization provides the ability to set a limit on disk I/O requests sent from the VMs to the host machine. This can prevent a VM from over-utilizing shared resources and impacting the performance of other VMs.

To enable disk I/O throttling, set a limit on disk I/O requests sent from each block device attached to VMs to the host machine.

Procedure

  1. Use the virsh domblklist command to list the names of all the disk devices on a specified VM. 

    # virsh domblklist rollin-coal
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/rollin-coal.qcow2
sda        -
sdb        /home/horridly-demanding-processes.iso

  2. Find the host block device where the virtual disk that you want to throttle is mounted.

    For example, if you want to throttle the sdb virtual disk from the previous step, the following output shows that the disk is mounted on the /dev/nvme0n1p3 partition. 

    $ lsblk
NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
zram0                                         252:0    0     4G  0 disk  [SWAP]
nvme0n1                                       259:0    0 238.5G  0 disk
├─nvme0n1p1                                   259:1    0   600M  0 part  /boot/efi
├─nvme0n1p2                                   259:2    0     1G  0 part  /boot
└─nvme0n1p3                                   259:3    0 236.9G  0 part
  └─luks-a1123911-6f37-463c-b4eb-fxzy1ac12fea 253:0    0 236.9G  0 crypt /home

  3. Set I/O limits for the block device using the virsh blkiotune command. 

    # virsh blkiotune VM-name --parameter device,limit

    The following example throttles the sdb disk on the rollin-coal VM to 1000 read and write I/O operations per second and to 50 MB per second read and write throughput. 

    # virsh blkiotune rollin-coal --device-read-iops-sec /dev/nvme0n1p3,1000 --device-write-iops-sec /dev/nvme0n1p3,1000 --device-write-bytes-sec /dev/nvme0n1p3,52428800 --device-read-bytes-sec /dev/nvme0n1p3,52428800

Additional information

  • Disk I/O throttling can be useful in various situations, for example when VMs belonging to different customers are running on the same host, or when quality of service guarantees are given for different VMs. Disk I/O throttling can also be used to simulate slower disks.
  • I/O throttling can be applied independently to each block device attached to a VM and supports limits on throughput and I/O operations.
  • Red Hat does not support using the virsh blkdeviotune command to configure I/O throttling in VMs. For more information on unsupported features when using RHEL 8 as a VM host, see Section 20.3, “Unsupported features in RHEL 8 virtualization”.

16.4.3. Enabling multi-queue virtio-scsi

When using virtio-scsi storage devices in your virtual machines (VMs), the multi-queue virtio-scsi feature provides improved storage performance and scalability. It enables each virtual CPU (vCPU) to have a separate queue and interrupt to use without affecting other vCPUs.

Procedure

  • To enable multi-queue virtio-scsi support for a specific VM, add the following to the VM’s XML configuration, where N is the total number of vCPU queues: 

    <controller type='scsi' index='0' model='virtio-scsi'>
   <driver queues='N' />
</controller>

16.5. Optimizing virtual machine CPU performance

Much like physical CPUs in host machines, vCPUs are critical to virtual machine (VM) performance. As a result, optimizing vCPUs can have a significant impact on the resource efficiency of your VMs. To optimize your vCPU:

  1. Adjust how many host CPUs are assigned to the VM. You can do this using the CLI or the web console.

  2. Ensure that the vCPU model is aligned with the CPU model of the host. For example, to set the testguest1 VM to use the CPU model of the host: 

    # virt-xml testguest1 --edit --cpu host-model
  3. Deactivate kernel same-page merging (KSM).

  4. If your host machine uses Non-Uniform Memory Access (NUMA), you can also configure NUMA for its VMs. This maps the host’s CPU and memory processes onto the CPU and memory processes of the VM as closely as possible. In effect, NUMA tuning provides the vCPU with a more streamlined access to the system memory allocated to the VM, which can improve the vCPU processing effectiveness.

    For details, see Section 16.5.3, “Configuring NUMA in a virtual machine” and Section 16.5.4, “Sample vCPU performance tuning scenario”.

16.5.1. Adding and removing virtual CPUs using the command-line interface

To increase or optimize the CPU performance of a virtual machine (VM), you can add or remove virtual CPUs (vCPUs) assigned to the VM.

When performed on a running VM, this is also referred to as vCPU hot plugging and hot unplugging. However, note that vCPU hot unplug is not supported in RHEL 8, and Red Hat highly discourages its use.

Prerequisites

  • Optional: View the current state of the vCPUs in the targeted VM. For example, to display the number of vCPUs on the testguest VM: 

    # virsh vcpucount testguest
maximum      config         4
maximum      live           2
current      config         2
current      live           1

    This output indicates that testguest is currently using 1 vCPU, and 1 more vCPu can be hot plugged to it to increase the VM’s performance. However, after reboot, the number of vCPUs testguest uses will change to 2, and it will be possible to hot plug 2 more vCPUs.

Procedure

  1. Adjust the maximum number of vCPUs that can be attached to a VM, which takes effect on the VM’s next boot.

    For example, to increase the maximum vCPU count for the testguest VM to 8: 

    # virsh setvcpus testguest 8 --maximum --config

    Note that the maximum may be limited by the CPU topology, host hardware, the hypervisor, and other factors.

  2. Adjust the current number of vCPUs attached to a VM, up to the maximum configured in the previous step. For example:

    • To increase the number of vCPUs attached to the running testguest VM to 4: 

      # virsh setvcpus testguest 4 --live

      This increases the VM’s performance and host load footprint of testguest until the VM’s next boot.

    • To permanently decrease the number of vCPUs attached to the testguest VM to 1: 

      # virsh setvcpus testguest 1 --config

      This decreases the VM’s performance and host load footprint of testguest after the VM’s next boot. However, if needed, additional vCPUs can be hot plugged to the VM to temporarily increase its performance.

Verification

  • Confirm that the current state of vCPU for the VM reflects your changes. 

    # virsh vcpucount testguest
maximum      config         8
maximum      live           4
current      config         1
current      live           4

Additional resources

16.5.2. Managing virtual CPUs using the web console

Using the RHEL 8 web console, you can review and configure virtual CPUs used by virtual machines (VMs) to which the web console is connected.

Prerequisites

Procedure

  1. In the Virtual Machines interface, click a row with the name of the VMs for which you want to view and configure virtual CPU parameters.

    The row expands to reveal the Overview pane with basic information about the selected VMs, including the number of virtual CPUs, and controls for shutting down and deleting the VM.

  2. Click the number of vCPUs in the Overview pane.

    The vCPU details dialog appears.

    cockpit configure vCPUs
    Note

    The warning in the vCPU details dialog only appears after the virtual CPU settings are changed.

  3. Configure the virtual CPUs for the selected VM.

    • vCPU Count - The number of vCPUs currently in use.

      Note

      The vCPU count cannot be greater than the vCPU Maximum.

    • vCPU Maximum - The maximum number of virtual CPUs that can be configured for the VM. If this value is higher than the vCPU Count, additional vCPUs can be attached to the VM.
    • Sockets - The number of sockets to expose to the VM.
    • Cores per socket - The number of cores for each socket to expose to the VM.

    • Threads per core - The number of threads for each core to expose to the VM.

      Note that the Sockets, Cores per socket, and Threads per core options adjust the CPU topology of the VM. This may be beneficial for vCPU performance and may impact the functionality of certain software in the guest OS. If a different setting is not required by your deployment, Red Hat recommends keeping the default values.

  4. Click Apply.

    The virtual CPUs for the VM are configured.

    Note

    Changes to virtual CPU settings only take effect after the VM is restarted.

Additional resources:

16.5.3. Configuring NUMA in a virtual machine

The following methods can be used to configure Non-Uniform Memory Access (NUMA) settings of a virtual machine (VM) on a RHEL 8 host.

Prerequisites

  • The host is a NUMA-compatible machine. To detect whether this is the case, use the virsh nodeinfo command and see the NUMA cell(s) line: 

    # virsh nodeinfo
CPU model:           x86_64
CPU(s):              48
CPU frequency:       1200 MHz
CPU socket(s):       1
Core(s) per socket:  12
Thread(s) per core:  2
NUMA cell(s):        2
Memory size:         67012964 KiB

    If the value of the line is 2 or greater, the host is NUMA-compatible.

Procedure

For ease of use, you can set up a VM’s NUMA configuration using automated utilities and services. However, manual NUMA setup is more likely to yield a significant performance improvement.

Automatic methods

  • Set the VM’s NUMA policy to Preferred. For example, to do so for the testguest5 VM: 

    # virt-xml testguest5 --edit --vcpus placement=auto
# virt-xml testguest5 --edit --numatune mode=preferred

  • Enable automatic NUMA balancing on the host: 

    # echo 1 > /proc/sys/kernel/numa_balancing

  • Use the numad command to automatically align the VM CPU with memory resources. 

    # numad

Manual methods

  1. Pin specific vCPU threads to a specific host CPU or range of CPUs. This is also possible on non-NUMA hosts and VMs, and is recommended as a safe method of vCPU performance improvement.

    For example, the following commands pin vCPU threads 0 to 5 of the testguest6 VM to host CPUs 1, 3, 5, 7, 9, and 11, respectively: 

    # virsh vcpupin testguest6 0 1
# virsh vcpupin testguest6 1 3
# virsh vcpupin testguest6 2 5
# virsh vcpupin testguest6 3 7
# virsh vcpupin testguest6 4 9
# virsh vcpupin testguest6 5 11

    Afterwards, you can verify whether this was successful: 

    # virsh vcpupin testguest6
VCPU   CPU Affinity
----------------------
0      1
1      3
2      5
3      7
4      9
5      11

  2. After pinning vCPU threads, you can also pin QEMU process threads associated with a specified VM to a specific host CPU or range of CPUs. For example, the following commands pin the QEMU process thread of testguest6 to CPUs 13 and 15, and verify this was successful: 

    # virsh emulatorpin testguest6 13,15
# virsh emulatorpin testguest6
emulator: CPU Affinity
----------------------------------
       *: 13,15

  3. Finally, you can also specify which host NUMA nodes will be assigned specifically to a certain VM. This can improve the host memory usage by the VM’s vCPU. For example, the following commands set testguest6 to use host NUMA nodes 3 to 5, and verify this was successful: 

    # virsh numatune testguest6 --nodeset 3-5
# virsh numatune testguest6

Additional resources

16.5.4. Sample vCPU performance tuning scenario

To obtain the best vCPU performance possible, Red Hat recommends using manual vcpupin, emulatorpin, and numatune settings together, for example like in the following scenario.

Starting scenario

  • Your host has the following hardware specifics:

    • 2 NUMA nodes
    • 3 CPU cores on each node
    • 2 threads on each core

    The output of virsh nodeinfo of such a machine would look similar to: 

    # virsh nodeinfo
CPU model:           x86_64
CPU(s):              12
CPU frequency:       3661 MHz
CPU socket(s):       2
Core(s) per socket:  3
Thread(s) per core:  2
NUMA cell(s):        2
Memory size:         31248692 KiB

  • You intend to modify an existing VM to have 8 vCPUs, which means that it will not fit in a single NUMA node.

    Therefore, you should distribute 4 vCPUs on each NUMA node and make the vCPU topology resemble the host topology as closely as possible. This means that vCPUs that run as sibling threads of a given physical CPU should be pinned to host threads on the same core. For details, see the Solution below:

Solution

  1. Obtain the information on the host topology: 

    # virsh capabilities

    The output should include a section that looks similar to the following: 

    <topology>
  <cells num="2">
    <cell id="0">
      <memory unit="KiB">15624346</memory>
      <pages unit="KiB" size="4">3906086</pages>
      <pages unit="KiB" size="2048">0</pages>
      <pages unit="KiB" size="1048576">0</pages>
      <distances>
        <sibling id="0" value="10" />
        <sibling id="1" value="21" />
      </distances>
      <cpus num="6">
        <cpu id="0" socket_id="0" core_id="0" siblings="0,3" />
        <cpu id="1" socket_id="0" core_id="1" siblings="1,4" />
        <cpu id="2" socket_id="0" core_id="2" siblings="2,5" />
        <cpu id="3" socket_id="0" core_id="0" siblings="0,3" />
        <cpu id="4" socket_id="0" core_id="1" siblings="1,4" />
        <cpu id="5" socket_id="0" core_id="2" siblings="2,5" />
      </cpus>
    </cell>
    <cell id="1">
      <memory unit="KiB">15624346</memory>
      <pages unit="KiB" size="4">3906086</pages>
      <pages unit="KiB" size="2048">0</pages>
      <pages unit="KiB" size="1048576">0</pages>
      <distances>
        <sibling id="0" value="21" />
        <sibling id="1" value="10" />
      </distances>
      <cpus num="6">
        <cpu id="6" socket_id="1" core_id="3" siblings="6,9" />
        <cpu id="7" socket_id="1" core_id="4" siblings="7,10" />
        <cpu id="8" socket_id="1" core_id="5" siblings="8,11" />
        <cpu id="9" socket_id="1" core_id="3" siblings="6,9" />
        <cpu id="10" socket_id="1" core_id="4" siblings="7,10" />
        <cpu id="11" socket_id="1" core_id="5" siblings="8,11" />
      </cpus>
    </cell>
  </cells>
</topology>
  2. Optional: Test the performance of the VM using the applicable tools and utilities.

  3. Set up and mount 1 GiB huge pages on the host:

    1. Add the following line to the host’s kernel command line: 

      default_hugepagesz=1G hugepagesz=1G

    2. Create the /etc/systemd/system/hugetlb-gigantic-pages.service file with the following content: 

      [Unit]
Description=HugeTLB Gigantic Pages Reservation
DefaultDependencies=no
Before=dev-hugepages.mount
ConditionPathExists=/sys/devices/system/node
ConditionKernelCommandLine=hugepagesz=1G

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/etc/systemd/hugetlb-reserve-pages.sh

[Install]
WantedBy=sysinit.target

    3. Create the /etc/systemd/hugetlb-reserve-pages.sh file with the following content: 

      #!/bin/sh

nodes_path=/sys/devices/system/node/
if [ ! -d $nodes_path ]; then
	echo "ERROR: $nodes_path does not exist"
	exit 1
fi

reserve_pages()
{
	echo $1 > $nodes_path/$2/hugepages/hugepages-1048576kB/nr_hugepages
}

reserve_pages 4 node1
reserve_pages 4 node2

      This reserves four 1GiB huge pages from node1 and four 1GiB huge pages from node2.

    4. Make the script created in the previous step executable: 

      # chmod +x /etc/systemd/hugetlb-reserve-pages.sh

    5. Enable huge page reservation on boot: 

      # systemctl enable hugetlb-gigantic-pages

  4. Use the virsh edit command to edit the XML configuration of the VM you wish to optimize, in this example super-VM: 

    # virsh edit super-vm

  5. Adjust the XML configuration of the VM in the following way:

    1. Set the VM to use 8 static vCPUs. Use the <vcpu/> element to do this.

    2. Pin each of the vCPU threads to the corresponding host CPU threads that it mirrors in the topology. To do so, use the <vcpupin/> elements in the <cputune> section.

      Note that, as shown by the virsh capabilities utility above, host CPU threads are not ordered sequentially in their respective cores. In addition, the vCPU threads should be pinned to the highest available set of host cores on the same NUMA node. For a table illustration, see the Additional Resources section below.

      The XML configuration for steps a. and b. can look similar to: 

      <cputune>
  <vcpupin vcpu='0' cpuset='1'/>
  <vcpupin vcpu='1' cpuset='4'/>
  <vcpupin vcpu='2' cpuset='2'/>
  <vcpupin vcpu='3' cpuset='5'/>
  <vcpupin vcpu='4' cpuset='7'/>
  <vcpupin vcpu='5' cpuset='10'/>
  <vcpupin vcpu='6' cpuset='8'/>
  <vcpupin vcpu='7' cpuset='11'/>
  <emulatorpin cpuset='6,9'/>
</cputune>

    3. Set the VM to use 1 GiB huge pages: 

      <memoryBacking>
  <hugepages>
    <page size='1' unit='GiB'/>
  </hugepages>
</memoryBacking>

    4. Configure the VM’s NUMA nodes to use memory from the corresponding NUMA nodes on the host. To do so, use the <memnode/> elements in the <numatune/> section: 

      <numatune>
  <memory mode="preferred" nodeset="1"/>
  <memnode cellid="0" mode="strict" nodeset="0"/>
  <memnode cellid="1" mode="strict" nodeset="1"/>
</numatune>

    5. Ensure the CPU mode is set to host-passthrough, and that the CPU uses cache in passthrough mode: 

      <cpu mode="host-passthrough">
  <topology sockets="2" cores="2" threads="2"/>
  <cache mode="passthrough"/>

  6. The resulting XML configuration of the VM should include a section similar to the following: 

    [...]
  <memoryBacking>
    <hugepages>
      <page size='1' unit='GiB'/>
    </hugepages>
  </memoryBacking>
  <vcpu placement='static'>8</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='1'/>
    <vcpupin vcpu='1' cpuset='4'/>
    <vcpupin vcpu='2' cpuset='2'/>
    <vcpupin vcpu='3' cpuset='5'/>
    <vcpupin vcpu='4' cpuset='7'/>
    <vcpupin vcpu='5' cpuset='10'/>
    <vcpupin vcpu='6' cpuset='8'/>
    <vcpupin vcpu='7' cpuset='11'/>
    <emulatorpin cpuset='6,9'/>
  </cputune>
  <numatune>
    <memory mode="preferred" nodeset="1"/>
    <memnode cellid="0" mode="strict" nodeset="0"/>
    <memnode cellid="1" mode="strict" nodeset="1"/>
  </numatune>
  <cpu mode="host-passthrough">
    <topology sockets="2" cores="2" threads="2"/>
    <cache mode="passthrough"/>
    <numa>
      <cell id="0" cpus="0-3" memory="2" unit="GiB">
        <distances>
          <sibling id="0" value="10"/>
          <sibling id="1" value="21"/>
        </distances>
      </cell>
      <cell id="1" cpus="4-7" memory="2" unit="GiB">
        <distances>
          <sibling id="0" value="21"/>
          <sibling id="1" value="10"/>
        </distances>
      </cell>
    </numa>
  </cpu>
</domain>
  7. Optional: Test the performance of the VM using the applicable tools and utilities to evaluate the impact of the VM’s optimization.

Additional resources

  • The following tables illustrate the connections between the vCPUs and the host CPUs they should be pinned to:

    Table 16.1. Host topology

    CPU threads

    0

    3

    1

    4

    2

    5

    6

    9

    7

    10

    8

    11

    Cores

    0

    1

    2

    3

    4

    5

    Sockets

    0

    1

    NUMA nodes

    0

    1

    Table 16.2. VM topology

    vCPU threads

    0

    1

    2

    3

    4

    5

    6

    7

    Cores

    0

    1

    2

    3

    Sockets

    0

    1

    NUMA nodes

    0

    1

    Table 16.3. Combined host and VM topology

    vCPU threads

    		 

    0

    1

    2

    3

    		 

    4

    5

    6

    7

    Host CPU threads

    0

    3

    1

    4

    2

    5

    6

    9

    7

    10

    8

    11

    Cores

    0

    1

    2

    3

    4

    5

    Sockets

    0

    1

    NUMA nodes

    0

    1

    In this scenario, there are 2 NUMA nodes and 8 vCPUs. Therefore, 4 vCPU threads should be pinned to each node.

    In addition, Red Hat recommends leaving at least a single CPU thread available on each node for host system operations.

    Because in this example, each NUMA node houses 3 cores, each with 2 host CPU threads, the set for node 0 translates as follows: 

    <vcpupin vcpu='0' cpuset='1'/>
<vcpupin vcpu='1' cpuset='4'/>
<vcpupin vcpu='2' cpuset='2'/>
<vcpupin vcpu='3' cpuset='5'/>

16.5.5. Deactivating kernel same-page merging

Although kernel same-page merging (KSM) improves memory density, it increases CPU utilization, and might adversely affect overall performance depending on the workload. In such cases, you can improve the virtual machine (VM) performance by deactivating KSM.

Depending on your requirements, you can either deactivate KSM for a single session or persistently.

Procedure

  • To deactivate KSM for a single session, use the systemctl utility to stop ksm and ksmtuned services. 

    # systemctl stop ksm

# systemctl stop ksmtuned

  • To deactivate KSM persistently, use the systemctl utility to disable ksm and ksmtuned services. 

    # systemctl disable ksm
Removed /etc/systemd/system/multi-user.target.wants/ksm.service.
# systemctl disable ksmtuned
Removed /etc/systemd/system/multi-user.target.wants/ksmtuned.service.
Note

Memory pages shared between VMs before deactivating KSM will remain shared. To stop sharing, delete all the PageKSM pages in the system using the following command: 

# echo 2 > /sys/kernel/mm/ksm/run

After anonymous pages replace the KSM pages, the khugepaged kernel service will rebuild transparent hugepages on the VM’s physical memory.

16.6. Optimizing virtual machine network performance

Due to the virtual nature of a VM’s network interface card (NIC), the VM loses a portion of its allocated host network bandwidth, which can reduce the overall workload efficiency of the VM. The following tips can minimize the negative impact of virtualization on the virtual NIC (vNIC) throughput.

Procedure

Use any of the following methods and observe if it has a beneficial effect on your VM network performance:

Enable the vhost_net module

On the host, ensure the vhost_net kernel feature is enabled: 

# lsmod | grep vhost
vhost_net              32768  1
vhost                  53248  1 vhost_net
tap                    24576  1 vhost_net
tun                    57344  6 vhost_net

If the output of this command is blank, enable the vhost_net kernel module: 

# modprobe vhost_net
Set up multi-queue virtio-net

To set up the multi-queue virtio-net feature for a VM, use the virsh edit command to edit to the XML configuration of the VM. In the XML, add the following to the <devices> section, and replace N with the number of vCPUs in the VM, up to 16: 

<interface type='network'>
      <source network='default'/>
      <model type='virtio'/>
      <driver name='vhost' queues='N'/>
</interface>

If the VM is running, restart it for the changes to take effect.

Batching network packets

In Linux VM configurations with a long transmission path, batching packets before submitting them to the kernel may improve cache utilization. To set up packet batching, use the following command on the host, and replace tap0 with the name of the network interface that the VMs use: 

# ethtool -C tap0 rx-frames 128
SR-IOV
If your host NIC supports SR-IOV, use SR-IOV device assignment for your vNICs. For more information, see Section 10.8, “Managing SR-IOV devices”.

Additional resources

16.7. Virtual machine performance monitoring tools

To identify what consumes the most VM resources and which aspect of VM performance needs optimization, performance diagnostic tools, both general and VM-specific, can be used.

Default OS performance monitoring tools

For standard performance evaluation, you can use the utilities provided by default by your host and guest operating systems:

  • On your RHEL 8 host, as root, use the top utility or the system monitor application, and look for qemu and virt in the output. This shows how much host system resources your VMs are consuming.

    • If the monitoring tool displays that any of the qemu or virt processes consume a large portion of the host CPU or memory capacity, use the perf utility to investigate. For details, see below.
    • In addition, if a vhost_net thread process, named for example vhost_net-1234, is displayed as consuming an excessive amount of host CPU capacity, consider using virtual network optimization features, such as multi-queue virtio-net.

  • On the guest operating system, use performance utilities and applications available on the system to evaluate which processes consume the most system resources.

    • On Linux systems, you can use the top utility.
    • On Windows systems, you can use the Task Manager application.

perf kvm

You can use the perf utility to collect and analyze virtualization-specific statistics about the performance of your RHEL 8 host. To do so:

  1. On the host, install the perf package: 

    # yum install perf

  2. Use one of the perf kvm stat commands to display perf statistics for your virtualization host:

    • For real-time monitoring of your hypervisor, use the perf kvm stat live command.
    • To log the perf data of your hypervisor over a period of time, activate the logging using the perf kvm stat record command. After the command is canceled or interrupted, the data is saved in the perf.data.guest file, which can be analyzed using the perf kvm stat report command.

  3. Analyze the perf output for types of VM-EXIT events and their distribution. For example, the PAUSE_INSTRUCTION events should be infrequent, but in the following output, the high occurrence of this event suggests that the host CPUs are not handling the running vCPUs well. In such a scenario, consider shutting down some of your active VMs, removing vCPUs from these VMs, or tuning the performance of the vCPUs. 

    # perf kvm stat report

Analyze events for all VMs, all VCPUs:


             VM-EXIT    Samples  Samples%     Time%    Min Time    Max Time         Avg time

  EXTERNAL_INTERRUPT     365634    31.59%    18.04%      0.42us  58780.59us    204.08us ( +-   0.99% )
           MSR_WRITE     293428    25.35%     0.13%      0.59us  17873.02us      1.80us ( +-   4.63% )
    PREEMPTION_TIMER     276162    23.86%     0.23%      0.51us  21396.03us      3.38us ( +-   5.19% )
   PAUSE_INSTRUCTION     189375    16.36%    11.75%      0.72us  29655.25us    256.77us ( +-   0.70% )
                 HLT      20440     1.77%    69.83%      0.62us  79319.41us  14134.56us ( +-   0.79% )
              VMCALL      12426     1.07%     0.03%      1.02us   5416.25us      8.77us ( +-   7.36% )
       EXCEPTION_NMI         27     0.00%     0.00%      0.69us      1.34us      0.98us ( +-   3.50% )
       EPT_MISCONFIG          5     0.00%     0.00%      5.15us     10.85us      7.88us ( +-  11.67% )

Total Samples:1157497, Total events handled time:413728274.66us.

    Other event types that can signal problems in the output of perf kvm stat include:

For more information on using perf to monitor virtualization performance, see the perf-kvm man page.

numastat

To see the current NUMA configuration of your system, you can use the numastat utility, which is provided by installing the numactl package.

The following shows a host with 4 running VMs, each obtaining memory from multiple NUMA nodes. This is not optimal for vCPU performance, and warrants adjusting: 

# numastat -c qemu-kvm

Per-node process memory usage (in MBs)
PID              Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total
---------------  ------ ------ ------ ------ ------ ------ ------ ------ -----
51722 (qemu-kvm)     68     16    357   6936      2      3    147    598  8128
51747 (qemu-kvm)    245     11      5     18   5172   2532      1     92  8076
53736 (qemu-kvm)     62    432   1661    506   4851    136     22    445  8116
53773 (qemu-kvm)   1393      3      1      2     12      0      0   6702  8114
---------------  ------ ------ ------ ------ ------ ------ ------ ------ -----
Total              1769    463   2024   7462  10037   2672    169   7837 32434

In contrast, the following shows memory being provided to each VM by a single node, which is significantly more efficient. 

# numastat -c qemu-kvm

Per-node process memory usage (in MBs)
PID              Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total
---------------  ------ ------ ------ ------ ------ ------ ------ ------ -----
51747 (qemu-kvm)      0      0      7      0   8072      0      1      0  8080
53736 (qemu-kvm)      0      0      7      0      0      0   8113      0  8120
53773 (qemu-kvm)      0      0      7      0      0      0      1   8110  8118
59065 (qemu-kvm)      0      0   8050      0      0      0      0      0  8051
---------------  ------ ------ ------ ------ ------ ------ ------ ------ -----
Total                 0      0   8072      0   8072      0   8114   8110 32368

Chapter 17. Installing and managing Windows virtual machines

To use Microsoft Windows as the guest operating system in your virtual machines (VMs) on a RHEL 8 host, Red Hat recommends taking extra steps to ensure these VMs run correctly.

For this purpose, the following sections provide information on installing and optimizing Windows VMs on the host, as well as installing and configuring drivers in these VMs.

17.1. Installing Windows virtual machines

The following provides information on how to create a fully-virtualized Windows machine on a RHEL 8 host, launch the graphical Windows installer inside the virtual machine (VM), and optimize the installed Windows guest operating system (OS).

You can create a VM and install it using the virt-install command or the RHEL 8 web console.

Prerequisites

Procedure

  1. Create the VM. For instructions, see Section 2.2, “Creating virtual machines”.

    • If using the virt-install utility to create the VM, add the following options to the command:

      • The storage medium with the KVM virtio drivers. For example: 

        --disk path=/usr/share/virtio-win/virtio-win.iso,device=disk,bus=virtio

      • The Windows version you will install. For example, for Windows 10: 

        --os-variant win10

        For a list of available Windows versions and the appropriate option, use the following command: 

        # osinfo-query os
    • If using the web console to create the VM, specify your version of Windows in the Operating System field of the Create New Virtual Machine window. After the VM is created and the guest OS is installed, attach the storage medium with virtio drivers to the VM using the Disks interface. For instructions, see Section 11.3.7.3, “Attaching existing disks to virtual machines using the web console”.

  2. Install the Windows OS in the VM.

    For information on how to install a Windows operating system, refer to the relevant Microsoft installation documentation.

  3. Configure KVM virtio drivers in the Windows guest OS. For details, see Section 17.2.1, “Installing KVM paravirtualized drivers for Windows virtual machines”.

Additional resources

17.2. Optimizing Windows virtual machines

When using Microsoft Windows as a guest operating system in a virtual machine (VM) hosted in RHEL 8, the performance of the guest may be negatively impacted.

Therefore, Red Hat recommends optimizing your Windows VMs by doing any combination of the following:

17.2.1. Installing KVM paravirtualized drivers for Windows virtual machines

The primary method of improving the performance of your Windows virtual machines (VMs) is to install KVM paravirtualized (virtio) drivers for Windows on the guest operating system (OS).

To do so:

  1. Prepare the install media on the host machine. For more information, see Section 17.2.1.2, “Preparing virtio driver installation media on a host machine”.
  2. Attach the install media to an existing Windows VM, or attach it when creating a new Windows VM.
  3. Install the virtio drivers on the Windows guest OS. For more information, see Section 17.2.1.3, “Installing virtio drivers on a Windows guest”.

17.2.1.1. How Windows virtio drivers work

Paravirtualized drivers enhance the performance of virtual machines (VMs) by decreasing I/O latency and increasing throughput to almost bare-metal levels. Red Hat recommends that you use paravirtualized drivers for VMs that run I/O-heavy tasks and applications.

virtio drivers are KVM’s paravirtualized device drivers, available for Windows VMs running on KVM hosts. These drivers are provided by the virtio-win package, which includes drivers for:

  • Block (storage) devices
  • Network interface controllers
  • Video controllers
  • Memory ballooning device
  • Paravirtual serial port device
  • Entropy source device
  • Paravirtual panic device
  • Input devices, such as mice, keyboards, or tablets
  • A small set of emulated devices
Note

For additional information about emulated, virtio, and assigned devices, refer to Chapter 10, Managing virtual devices.

Using KVM virtio drivers, the following Microsoft Windows versions are expected to run similarly to physical systems:

17.2.1.2. Preparing virtio driver installation media on a host machine

To install KVM virtio drivers on a Windows virtual machine (VM), you must first prepare the installation media for the virtio driver on the host machine. To do so, install the virtio-win package on the host machine and use the .iso file it provides as storage for the VM.

Prerequisites

  • Ensure that virtualization is enabled in your RHEL 8 host system.

Procedure

  1. Download the drivers

    1. Browse to Download Red Hat Enterprise Linux.
    2. Select the Product Variant relevant for your system architecture. For example, for Intel 64 and AMD64, select Red Hat Enterprise Linux for x86_64.
    3. Ensure the Version is 8.
    4. In the Packages, search for virtio-win.

    5. Click Download Latest.

      The RPM file downloads.

  2. Install the virtio-win package from the download directory. For example: 

    # yum install ~/Downloads/virtio-win-1.9.9-3.el8.noarch.rpm
[...]
Installed:
  virtio-win-1.9.9-3.el8.noarch

    If the installation succeeds, the virtio-win driver files are prepared in the /usr/share/virtio-win/ directory. These include ISO files and a drivers directory with the driver files in directories, one for each architecture and supported Windows version. 

    # ls /usr/share/virtio-win/
drivers/  guest-agent/  virtio-win-1.9.9.iso  virtio-win.iso

  3. Attach the virtio-win.iso file to the Windows VM. To do so, do one of the following:

    • Use the file as a disk when creating a new Windows VM.

    • Add the file as a CD-ROM to an existing Windows VM. For example: 

      # virt-xml WindowsVM --add-device --disk virtio-win.iso,device=cdrom
Domain 'WindowsVM' defined successfully.

Additional resources

17.2.1.3. Installing virtio drivers on a Windows guest

To install KVM virtio drivers on a Windows guest operating system (OS), you must add a storage device that contains the drivers - either when creating the virtual machine (VM) or afterwards - and install the drivers in the Windows guest OS.

Prerequisites

Procedure

  1. In the Windows guest OS, open the File Explorer application.
  2. Click This PC.
  3. In the Devices and drives pane, open the virtio-win medium.

  4. Based on the architecture of the VM’s vCPU, run one of the installers on the medium.

    • If using a 32-bit vCPU, run the virtio-win-gt-x86 installer.
    • If using a 64-bit vCPU, run the virtio-win-gt-x64 installer.
    virtio win installer 1

  5. In the Virtio-win-guest-tools setup wizard that opens, follow the displayed instructions until you reach the Custom Setup step.

    virtio win installer 2
  6. In the Custom Setup window, select the device drivers you want to install. The recommended driver set is selected automatically, and the descriptions of the drivers are displayed on the right of the list.
  7. Click next, then click Install.
  8. After the installation completes, click Finish.
  9. Reboot the VM to complete the driver installation.

Verification

  1. In This PC, open the system disk. This is typically (C:).

  2. In the Program Files directory, open the Virtio-Win directory.

    If the Virtio-Win directory is present and contains a sub-directory for each of the selected drivers, the installation was successful.

    virtio win installer 3

Additional resources

17.2.2. Enabling Hyper-V enlightenments

Hyper-V enlightenments provide a method for KVM to emulate the Microsoft Hyper-V hypervisor. This improves the performance of Windows virtual machines.

The following sections provide information about the supported Hyper-V enlightenments and how to enable them.

17.2.2.1. Enabling Hyper-V enlightenments on a Windows virtual machine

Hyper-V enlightenments provide better performance in a Windows virtual machine (VM) running in a RHEL 8 host. For instructions on how to enable them, see the following.

Procedure

  1. Use the virsh edit command to open the XML configuration of the VM. For example: 

    # virsh edit windows-vm

  2. Add the following lines to the XML: 

    <hyperv>
  <relaxed state='on'/>
  <vapic state='on'/>
  <spinlocks state='on' retries='8191'/>
  <vpindex state='on'/>
  <runtime state='on' />
  <synic state='on'/>
  <stimer state='on'/>
  <frequencies state='on'/>
</hyperv>

  3. Change the clock section of the configuration as follows: 

    <clock offset='localtime'>
  <timer name='hypervclock' present='yes'/>
</clock>
  4. Save and exit the XML configuration.
  5. If the VM is running, restart it.

Verification

  • Use the virsh dumpxml command to display the XML configuration of the running VM. If it includes the following segments, the Hyper-V enlightenments are enabled on the VM. 

    <hyperv>
  <relaxed state='on'/>
  <vapic state='on'/>
  <spinlocks state='on' retries='8191'/>
  <vpindex state='on'/>
  <runtime state='on' />
  <synic state='on'/>
  <stimer state='on'/>
  <frequencies state='on'/>
</hyperv>

<clock offset='localtime'>
  <timer name='hypervclock' present='yes'/>
</clock>

17.2.2.2. Configurable Hyper-V enlightenments

You can configure certain Hyper-V features to optimize Windows VMs. The following table provides information about these configurable Hyper-V features and their values.

Table 17.1. Configurable Hyper-V features

EnlightenmentDescriptionValues

evmcs

Implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) hypervisors, which enables faster L2 exits to the hypervisor. This feature is exclusive to Intel processors.

on, off

frequencies

Enables Hyper-V frequency Machine Specific Registers (MSRs).

on, off

ipi

Enables paravirtualized inter processor interrupts (IPI) support.

on, off

no-nonarch-coresharing

Notifies the guest OS that virtual processors will never share a physical core unless they are reported as sibling SMT threads. This information is required by Windows and Hyper-V guests to properly mitigate simultaneous multithreading (SMT) related CPU vulnerabilities.

on, off, auto

reenlightenment

Notifies when there is a time stamp counter (TSC) frequency change which only occurs during migration. It also allows the guest to keep using the old frequency until it is ready to switch to the new one.

on, off

relaxed

Disables a Windows sanity check that commonly results in a BSOD when the VM is running on a heavily loaded host. This is similar to the Linux kernel option no_timer_check, which is automatically enabled when Linux is running on KVM.

on, off

reset

Enables Hyper-V reset.

on, off

runtime

Sets processor time spent on running the guest code, and on behalf of the guest code.

on, off

spinlock

  • Used by a VM’s operating system to notify Hyper-V that the calling virtual processor is attempting to acquire a resource that is potentially held by another virtual processor within the same partition.
  • Used by Hyper-V to indicate to the virtual machine’s operating system the number of times a spinlock acquisition should be attempted before indicating an excessive spin situation to Hyper-V.

on, off

stimer

Enables synthetic timers for virtual processors. Note that certain Windows versions revert to using HPET (or even RTC when HPET is unavailable) when this enlightenment is not provided, which can lead to significant CPU consumption, even when the virtual CPU is idle.

on, off

stimer-direct

Enables synthetic timers when an expiration event is delivered via a normal interrupt.

on, off.

synic

Together with stimer, activates the synthetic timer. Windows 8 uses this feature in periodic mode.

on, off

time

Enables the following Hyper-V-specific clock sources available to the VM,

  • MSR-based 82 Hyper-V clock source (HV_X64_MSR_TIME_REF_COUNT, 0x40000020)
  • Reference TSC 83 page which is enabled via MSR (HV_X64_MSR_REFERENCE_TSC, 0x40000021)

on, off

tlbflush

Flushes the TLB of the virtual processors.

on, off

vapic

Enables virtual APIC, which provides accelerated MSR access to the high-usage, memory-mapped Advanced Programmable Interrupt Controller (APIC) registers.

on, off

vendor_id

Sets the Hyper-V vendor id.

  • on, off
  • Id value - string of up to 12 characters

vpindex

Enables virtual processor index.

on, off

17.2.3. Configuring NetKVM driver parameters

After the NetKVM driver is installed, you can configure it to better suit your environment. The parameters listed in this section can be configured using the Windows Device Manager (devmgmt.msc).

Important

Modifying the driver’s parameters causes Windows to reload that driver. This interrupts existing network activity.

Prerequisites

Procedure

  1. Open Windows Device Manager.

    For information on opening Device Manager, refer to the Windows documentation.

  2. Locate the Red Hat VirtIO Ethernet Adapter.

    1. In the Device Manager window, click + next to Network adapters.
    2. Under the list of network adapters, double-click Red Hat VirtIO Ethernet Adapter. The Properties window for the device opens.

  3. View the device parameters.

    In the Properties window, click the Advanced tab.

  4. Modify the device parameters.

    1. Click the parameter you want to modify. Options for that parameter are displayed.

    2. Modify the options as needed.

      For information on the NetKVM parameter options, refer to Section 17.2.4, “NetKVM driver parameters”.

    3. Click OK to save the changes.

17.2.4. NetKVM driver parameters

The following table provides information on the configurable NetKVM driver logging parameters.

Table 17.2. Logging parameters

ParameterDescription 2

Logging.Enable

A Boolean value that determines whether logging is enabled. The default value is Enabled.

Logging.Level

An integer that defines the logging level. As the integer increases, so does the verbosity of the log.

  • The default value is 0 (errors only).
  • 1-2 adds configuration messages.
  • 3-4 adds packet flow information.
  • 5-6 adds interrupt and DPC level trace information.
Note

High logging levels will slow down your virtual machine.

The following table provides information on the configurable NetKVM driver initial parameters.

Table 17.3. Initial parameters

ParameterDescription

Assign MAC

A string that defines the locally-administered MAC address for the paravirtualized NIC. This is not set by default.

Init.ConnectionRate(Mb)

An integer that represents the connection rate in megabits per second. The default value for Windows 2008 and later is 10G (10,000 megabits per second).

Init.Do802.1PQ

A Boolean value that enables Priority/VLAN tag population and removal support. The default value is Enabled.

Init.MTUSize

An integer that defines the maximum transmission unit (MTU). The default value is 1500. Any value from 500 to 65500 is acceptable.

Init.MaxTxBuffers

An integer that represents the number of TX ring descriptors that will be allocated.

The default value is 1024.

Valid values are: 16, 32, 64, 128, 256, 512, and 1024.

Init.MaxRxBuffers

An integer that represents the number of RX ring descriptors that will be allocated.

The default value is 256.

Valid values are: 16, 32, 64, 128, 256, 512, and 1024.

Offload.Tx.Checksum

Specifies the TX checksum offloading mode.

In Red Hat Enterprise Linux 8, the valid values for this parameter are:

* All (the default) which enables IP, TCP, and UDP checksum offloading for both IPv4 and IPv6

* TCP/UDP(v4,v6) which enables TCP and UDP checksum offloading for both IPv4 and IPv6

* TCP/UDP(v4) which enables TCP and UDP checksum offloading for IPv4 only

* TCP(v4) which enables only TCP checksum offloading for IPv4 only

17.2.5. Optimizing background processes on Windows virtual machines

To optimize the performance of a virtual machine (VM) running a Windows OS, you can configure or disable a variety of Windows processes.

Warning

Certain processes might not work as expected if you change their configuration.

Procedure

You can optimize your Windows VMs by performing any combination of the following:

  • Remove unused devices, such as USBs or CD-ROMs, and disable the ports.

  • Disable automatic Windows Update. For more information on how to do so, see Configure Group Policy Settings for Automatic Updates or Configure Windows Update for Business.

    Note that Windows Update is essential for installing latest updates and hotfixes from Microsoft. As such, Red Hat does not recommend disabling Windows Updates

  • Disable background services, such as SuperFetch and Windows Search. For more information about stopping services, see Disabling system services or Stop-Service.

  • Disable useplatformclock. To do so, run the following command, 

    # bcdedit /set useplatformclock No
  • Review and disable unnecessary scheduled tasks, such as scheduled disk defragmentation. For more information on how to do so, see Disable Scheduled Tasks.
  • Make sure the disks are not encrypted.
  • Reduce periodic activity of server applications. You can do so by editing the respective timers. For more information, see Multimedia Timers.
  • Close the Server Manager application on the VM.
  • Disable the antivirus software. Note that disabling the antivirus might compromise the security of the VM.
  • Disable the screen saver.
  • Keep the Windows OS on the sign-in screen when not in use.

Chapter 18. Creating nested virtual machines

RHEL 8.2 and later provide full support for the KVM nested virtualization feature on Intel hosts. This makes it possible for a virtual machine (also referred to as a level 1, or L1) that runs on a RHEL 8 physical host (level 0, or L0) to act as a hypervisor and create its own virtual machines (level 2 or L2).

In other words, a RHEL 8 host can run L1 virtual machines (VMs), and each of these VMs can host nested L2 VMs.

Nested virtualization is not recommended in production user environments, as it is subject to various limitations in functionality. Instead, nested virtualization is primarily intended for development and testing, for which it can be useful in a variety of scenarios, such as:

  • Debugging hypervisors in a constrained environment
  • Testing larger virtual deployments on a limited amount of physical resources

It is possible to create nested VMs on multiple architectures, but Red Hat currently supports nested VMs only on Intel systems. In contrast, nested virtualization on AMD, IBM POWER9, and IBM Z systems is only provided as a Technology Preview and is therefore unsupported.

18.1. Creating a nested virtual machine on Intel

Follow the steps below to enable and configure nested virtualization on an Intel host.

Prerequisites

  • An L0 RHEL8 host running an L1 virtual machine (VM).
  • The hypervisor CPU must support nested virtualization. To verify, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the vmx and ept flags, creating L2 VMs is possible. This is generally the case on Intel Xeon v3 cores and later.

  • Ensure that nested virtualization is enabled on the L0 host: 

    # cat /sys/module/kvm_intel/parameters/nested
    • If the command returns 1, the feature is enabled, and you can start the Procedure below..

    • If the command returns 0 or N but your system supports nested virtualization, use the following steps to enable the feature.

      1. Unload the kvm_intel module: 

        # modprobe -r kvm_intel

      2. Activate the nesting feature: 

        # modprobe kvm_intel nested=1

      3. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following line to the /etc/modprobe.d/kvm.conf file: 

        options kvm_intel nested=1

Procedure

  1. Configure your L1 VM for nested virtualization.

    1. Open the XML configuration of the VM. The following example opens the configuration of the Intel-L1 VM: 

      # virsh edit Intel-L1

    2. Add the following line to the configuration: 

      <cpu mode='host-passthrough'/>

      If the VM’s XML configuration file already contains a <cpu> element, rewrite it.

  2. Create an L2 VM within the L1 VM. To do this, follow the same procedure as when creating the L1 VM.

18.2. Creating a nested virtual machine on AMD

Follow the steps below to enable and configure nested virtualization on an AMD host.

Warning

Nested virtualization is currently provided only as a Technology Preview on the AMD64 architecture, and is therefore unsupported.

Prerequisites

  • An L0 RHEL8 host running an L1 virtual machine (VM).
  • The hypervisor CPU must support nested virtualization. To verify, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the svm and npt flags, creating L2 VMs is possible. This is generally the case on AMD EPYC cores and later.

  • Ensure that nested virtualization is enabled on the L0 host: 

    # cat /sys/module/kvm_amd/parameters/nested
    • If the command returns Y or 1, the feature is enabled, and you can start the Procedure below..

    • If the command returns 0 or N, use the following steps to enable the feature.

      1. Stop all running VMs on the L0 host.

      2. Unload the kvm_amd module: 

        # modprobe -r kvm_amd

      3. Activate the nesting feature: 

        # modprobe kvm_amd nested=1

      4. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following to the /etc/modprobe.d/kvm.conf file: 

        options kvm_amd nested=1

Procedure

  1. Configure your L1 VM for nested virtualization.

    1. Open the XML configuration of the VM. The following example opens the configuration of the AMD-L1 VM: 

      # virsh edit AMD-L1

    2. Configure the VM’s CPU to use host-passthrough mode. 

      <cpu mode='host-passthrough'/>

      If you require the VM to use a specific CPU instead of host-passthrough, add a <feature policy='require' name='vmx'/> line to the CPU configuration. For example: 

      <cpu mode ='custom' match ='exact' check='partial'>
<model fallback='allow'>Haswell-noTSX</model>
<feature policy='require' name='vmx'/>
  2. Create an L2 VM within the L1 VM. To do this, follow the same procedure as when creating the L1 VM.

18.3. Creating a nested virtual machine on IBM Z

Follow the steps below to enable and configure nested virtualization on an IBM Z host.

Warning

Nested virtualization is currently provided only as a Technology Preview on the IBM Z architecture, and is therefore unsupported.

Prerequisites

  • An L0 RHEL8 host running an L1 virtual machine (VM).
  • The hypervisor CPU must support nested virtualization. To verify this is the case, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the sie flag, creating L2 VMs is possible.

  • Ensure that nested virtualization is enabled on the L0 host: 

    # cat /sys/module/kvm/parameters/nested
    • If the command returns Y or 1, the feature is enabled, and you can start the Procedure below..

    • If the command returns 0 or N, use the following steps to enable the feature.

      1. Stop all running VMs on the L0 host.

      2. Unload the kvm module: 

        # modprobe -r kvm

      3. Activate the nesting feature: 

        # modprobe kvm nested=1

      4. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following line to the /etc/modprobe.d/kvm.conf file: 

        options kvm nested=1

Procedure

  • Create an L2 VM within the L1 VM. To do this, follow the same procedure as when creating the L1 VM.

18.4. Creating a nested virtual machine on IBM POWER9

Follow the steps below to enable and configure nested virtualization on an IBM POWER9 host.

Warning

Nested virtualization is currently provided only as a Technology Preview on the IBM POWER9 architecture, and is therefore unsupported. In addition, creating nested virtual machines (VMs) is not possible on previous versions of IBM POWER systems, such as IBM POWER8.

Prerequisites

  • An L0 RHEL8 host is running an L1 VM. The L1 VM is using RHEL 8 as the guest operating system.

  • Nested virtualization is enabled on the L0 host: 

    # cat /sys/module/kvm_hv/parameters/nested
    • If the command returns Y or 1, the feature is enabled, and you can start the Procedure below.

    • If the command returns 0 or N, use the following steps to enable the feature:

      1. Stop all running VMs on the L0 host.

      2. Unload the kvm module: 

        # modprobe -r kvm_hv

      3. Activate the nesting feature: 

        # modprobe kvm_hv nested=1

      4. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following line to the /etc/modprobe.d/kvm.conf file: 

        options kvm_hv nested=1

Procedure

  1. To ensure that the L1 VM can create L2 VMs, add the cap-nested-hv parameter to the machine type of the L1 VM. To do so, use the virsh edit command to modify the L1 VM’s XML configuration, and the following line to the <features> section: 

    <nested-hv state='on'/>

  2. Create an L2 VM within the L1 VM. To do this, follow the same procedure as when creating the L1 VM.

    To significantly improve the performance of L2 VMs, Red Hat recommends adding the`cap-nested-hv` parameter to the XML configurations of L2 VMs as well. For instructions, see the previous step.

Additional information

  • Note that using IBM POWER8 as the architecture for the L2 VM currently does not work.

18.5. Restrictions and limitations for nested virtualization

Keep the following restrictions in mind when using nested virtualization.

Supported architectures

  • The L0 host must be an Intel, AMD, IBM POWER9, or IBM Z system. Nested virtualization currently does not work on other architectures. In addition, Red Hat currently only supports Intel as a host for nested virtual machines (VMs), and all other architectures are provided only as Technology Previews.

Supported guest operating systems

  • For nested virtualization to be supported, you must use the following guest operating systems (OSs):

    • On the L0 host - RHEL 8.2 and later

    • On the L1 VMs - RHEL 7.8 and later, or RHEL 8.2 and later

      Note

      This support does not apply to using virtualization offerings based on RHEL 7 and RHEL 8 in L1 VMs. These include:

      • Red Hat Virtualization
      • Red Hat OpenStack Platform
      • OpenShift Virtualization

    • On the L2 VMs - you must use one of the following OSs:

      • RHEL 7.8 and later
      • RHEL 8.2 and later
      • Microsoft Windows Server 2016
      • Microsoft Windows Server 2019

  • In addition, on IBM POWER9, nested virtualization currently only works under the following circumstances:

    • Both the L0 host and the L1 VM use RHEL 8
    • The L2 VM uses RHEL 8, or RHEL 7 with a rhel-alt kernel.
    • The L1 VM and L2 VM are not running in POWER8 compatibility mode.

Non-KVM hypervisors

  • When using an L1 RHEL 8 VM on a non-KVM L0 hypervisor, such as VMware ESXi or Amazon Web Services (AWS), creating L2 VMs in the RHEL 8 guest OS may work, but is not supported.

Feature limitations

  • Use of L2 VMs as hypervisors and creating L3 guests has not been properly tested and is not expected to work.
  • Migrating VMs currently does not work on AMD systems if nested virtualization has been enabled on the L0 host.

  • On an IBM Z system, huge-page backing storage and nested virtualization cannot be used at the same time. 

    # modprobe kvm hpage=1 nested=1
modprobe: ERROR: could not insert 'kvm': Invalid argument
# dmesg |tail -1
[90226.508366] kvm-s390: A KVM host that supports nesting cannot back its KVM guests with huge pages

  • Some features available on the L0 host may be unavailable for the L1 hypervisor.

    For example, on IBM POWER 9 hardware, the External Interrupt Virtualization Engine (XIVE) does not work. However, L1 VMs can use the emulated XIVE interrupt controller to launch L2 VMs.

Chapter 19. Diagnosing virtual machine problems

When working with virtual machines (VMs), you may encounter problems with varying levels of severity. Some problems may have a quick and easy fix, while for others, you may have to capture VM-related data and logs to report or diagnose the problems.

The following sections provide detailed information about generating logs and diagnosing some common VM problems, as well as about reporting these problems.

19.1. Generating virtual machine debug logs

To diagnose virtual machine (VM) problems, it is helpful to generate and review the debug logs. Attaching debug logs is also useful when asking for support to resolve VM-related problems.

The following sections explain what debug logs are, how you can set them to be persistent, enable them during runtime, and attach them when reporting problems.

19.1.1. Understanding virtual machine debug logs

Debug logs are text files that contain data about events that occur during virtual machine (VM) runtime. The logs provide information about fundamental server-side functionalities, such as host libraries and the libvirtd service. The log files also contain the standard error output (stderr) of all running VMs.

Debug logging is not enabled by default and has to be enabled when libvirt starts. You can enable logging for a single session or persistently. You can also enable logging when a libvirtd daemon session is already running by modifying the daemon run-time settings.

Attaching the libvirt debug logs is also useful when requesting support with a VM problem.

19.1.2. Enabling persistent settings for virtual machine debug logs

You can configure virtual machine (VM) debug logging to be automatically enabled whenever libvirt starts by editing the libvirtd.conf configuration file which is located in the /etc/libvirt directory.

Procedure

  1. Open the libvirtd.conf file in an editor.

  2. Replace or set the filters according to your requirements.

    Setting the filter value to:

    • 1: logs all messages generated by libvirt.
    • 2: logs all non-debugging information.
    • 3: logs all warning and error messages. This is the default value.
    • 4: logs only error messages.

    For example, the following command:

    • Logs all error and warning messages from the remote, util.json, and rpc layers
    • Logs only error messages from the event layer.

    • Saves the filtered logs to /var/log/libvirt/libvirtd.log 

      log_filters="3:remote 4:event 3:util.json 3:rpc"
log_outputs="1:file:/var/log/libvirt/libvirtd.log"
  3. Save and exit.

  4. Restart the libvirtd service. 

    $ systemctl restart libvirtd.service

19.1.3. Enabling virtual machine debug logs during runtime

You can modify the libvirt daemon’s runtime settings to enable debug logs and save them to an output file.

This is useful when restarting libvirtd is not possible because restarting fixes the problem, or because there is another process, such as migration or backup, running at the same time. Modifying runtime settings is also useful if you want to try a command without editing the configuration files or restarting the daemon.

Prerequisites

  • Make sure the libvirt-admin package is installed.

Procedure

  1. Optional: Back up the active set of log filters. 

    # virt-admin daemon-log-filters >> virt-filters-backup
    Note

    It is recommended that you back up the active set of filters so that you can restore them after generating the logs. If you do not restore the filters, the messages will continue to be logged which may affect system performance.

  2. Use the virt-admin utility to enable debugging and set the filters according to your requirements.

    Setting the filter value to:

    • 1: logs all messages generated by libvirt.
    • 2: logs all non-debugging information.
    • 3: logs all warning and error messages. This is the default value.
    • 4: logs only error messages.

    For example, the following command:

    • Logs all error and warning messages from the remote, util.json, and rpc layers

    • Logs only error messages from the event layer. 

      # virt-admin daemon-log-filters "3:remote 4:event 3:util.json 3:rpc"

  3. Use the virt-admin utility to save the logs to a specific file or directory.
    For example, the following command saves the log output to the libvirt.log file in the /var/log/libvirt/ directory. 

    # virt-admin daemon-log-outputs "1:file:/var/log/libvirt/libvirtd.log"

  4. Optional: You can also remove the filters to generate a log file that contains all VM-related information. However, it is not recommended since this file may contain a large amount of redundant information produced by libvirt’s modules.

    • Use the virt-admin utility to specify an empty set of filters. 

      # virt-admin daemon-log-filters
  Logging filters:
  5. Optional: Restore the filters to their original state using the backup file.
    Perform the second step with the saved values to restore the filters.

19.1.4. Attaching virtual machine debug logs to support requests

You may have to request additional support to diagnose and resolve virtual machine (VM) problems. Attaching the debug logs to the support request is highly recommended to ensure that the support team has access to all the information they need to provide a quick resolution of the VM-related problem.

Procedure

  • To report a problem and request support, open a support case.

  • Based on the encountered problems, attach the following logs along with your report:

    • For problems with the libvirt service, attach the /var/log/libvirt/libvirtd.log file from the host.

    • For problems with a specific VM, attach its respective log file.

      For example, for the testguest1 VM, attach the testguest1.log file, which can be found at /var/log/libvirt/qemu/testguest1.log.

Additional resources

19.2. Dumping a virtual machine core

To analyze why a virtual machine (VM) crashed or malfunctioned, you can dump the VM core to a file on disk for later analysis and diagnostics.

This section provides a brief introduction to core dumping and explains how you can dump a VM core to a specific file.

19.2.1. How virtual machine core dumping works

A virtual machine (VM) requires numerous running processes to work accurately and efficiently. In some cases, a running VM may terminate unexpectedly or malfunction while you are using it. Restarting the VM may cause the data to be reset or lost, which makes it difficult to diagnose the exact problem that caused the VM to crash.

In such cases, you can use the virsh dump utility to save (or dump) the core of a VM to a file before you reboot the VM. The core dump file contains a raw physical memory image of the VM which contains detailed information about the VM. This information can be used to diagnose VM problems, either manually, or by using a tool such as the crash utility.

Additional resources

19.2.2. Creating a virtual machine core dump file

A virtual machine (VM) core dump contains detailed information about the state of a VM at any given time. This information, essentially a snapshot of the VM, is extremely useful to detect problems in the event of a VM malfunction or a sudden VM shutdown.

Prerequisites

  • Make sure you have sufficient disk space to save the file. Note that the space occupied by the VM depends on the amount of RAM allocated to the VM.

Procedure

  • Use the virsh dump utility.

    For example, the following command dumps the lander1 VM’s cores, its memory and the CPU common register file to gargantua.file in the /core/file directory. 

    # virsh dump lander1 /core/file/gargantua.file --memory-only
  Domain lander1 dumped to /core/file/gargantua.file
Important

The crash utility no longer supports the default file format of the virsh dump command. To analyze a core dump file using crash, you must create the file using the --memory-only option.

Additionally, you must use the --memory-only option when creating a core dump file to attach to a Red Hat Suport Case.

Additional resources