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Chapter 7. Virtualization

Increased Maximum Number of vCPUs in KVM

The maximum number of supported virtual CPUs (vCPUs) in a KVM guest has been increased to 240. This increases the amount of virtual processing units that a user can assign to the guest, and therefore improves its performance potential.

5th Generation Intel Core New Instructions Support in QEMU, KVM, and libvirt API

In Red Hat Enterprise Linux 7.1, the support for 5th Generation Intel Core processors has been added to the QEMU hypervisor, the KVM kernel code, and the libvirt API. This allows KVM guests to use the following instructions and features: ADCX, ADOX, RDSFEED, PREFETCHW, and supervisor mode access prevention (SMAP).

USB 3.0 Support for KVM Guests

Red Hat Enterprise Linux 7.1 features improved USB support by adding USB 3.0 host adapter (xHCI) emulation as a Technology Preview.

Compression for the dump-guest-memory Command

Since Red Hat Enterprise Linux 7.1, the dump-guest-memory command supports crash dump compression. This makes it possible for users who cannot use the virsh dump command to require less hard disk space for guest crash dumps. In addition, saving a compressed guest crash dump usually takes less time than saving a non-compressed one.

Open Virtual Machine Firmware

The Open Virtual Machine Firmware (OVMF) is available as a Technology Preview in Red Hat Enterprise Linux 7.1. OVMF is a UEFI secure boot environment for AMD64 and Intel 64 guests.

Improve Network Performance on Hyper-V

Several new features of the Hyper-V network driver have been introduced to improve network performance. For example, Receive-Side Scaling, Large Send Offload, Scatter/Gather I/O are now supported, and network throughput is increased.

hypervfcopyd in hyperv-daemons

The hypervfcopyd daemon has been added to the hyperv-daemons packages. hypervfcopyd is an implementation of file copy service functionality for Linux Guest running on Hyper-V 2012 R2 host. It enables the host to copy a file (over VMBUS) into the Linux Guest.

New Features in libguestfs

Red Hat Enterprise Linux 7.1 introduces a number of new features in libguestfs, a set of tools for accessing and modifying virtual machine disk images. Namely:
  • virt-builder — a new tool for building virtual machine images. Use virt-builder to rapidly and securely create guests and customize them.
  • virt-customize — a new tool for customizing virtual machine disk images. Use virt-customize to install packages, edit configuration files, run scripts, and set passwords.
  • virt-diff — a new tool for showing differences between the file systems of two virtual machines. Use virt-diff to easily discover what files have been changed between snapshots.
  • virt-log — a new tool for listing log files from guests. The virt-log tool supports a variety of guests including Linux traditional, Linux using journal, and Windows event log.
  • virt-v2v — a new tool for converting guests from a foreign hypervisor to run on KVM, managed by libvirt, OpenStack, oVirt, Red Hat Enterprise Virtualization (RHEV), and several other targets. Currently, virt-v2v can convert Red Hat Enterprise Linux and Windows guests running on Xen and VMware ESX.

Flight Recorder Tracing

Support for flight recorder tracing has been introduced in Red Hat Enterprise Linux 7.1. Flight recorder tracing uses SystemTap to automatically capture qemu-kvm data as long as the guest machine is running. This provides an additional avenue for investigating qemu-kvm problems, more flexible than qemu-kvm core dumps.
For detailed instructions on how to configure and use flight recorder tracing, see the Virtualization Deployment and Administration Guide.

LPAR Watchdog for IBM System z

As a Technology Preview, Red Hat Enterprise Linux 7.1 introduces a new watchdog driver for IBM System z. This enhanced watchdog supports Linux logical partitions (LPAR) as well as Linux guests in the z/VM hypervisor, and provides automatic reboot and automatic dump capabilities if a Linux system becomes unresponsive.

RDMA-based Migration of Live Guests

The support for Remote Direct Memory Access (RDMA)-based migration has been added to libvirt. As a result, it is now possible to use the new rdma:// migration URI to request migration over RDMA, which allows for significantly shorter live migration of large guests. Note that prior to using RDMA-based migration, RDMA has to be configured and libvirt has to be set up to use it.

Removal of Q35 Chipset, PCI Express Bus, and AHCI Bus Emulation

Red Hat Enterprise Linux 7.1 removes the emulation of the Q35 machine type, required also for supporting the PCI Express (PCIe) bus and the Advanced Host Controller Interface (AHCI) bus in KVM guest virtual machines. These features were previously available on Red Hat Enterprise Linux as Technology Previews. However, they are still being actively developed and might become available in the future as part of Red Hat products.