Chapter 3. Preparing Storage for Red Hat Virtualization

You need to prepare storage to be used for storage domains in the new environment. A Red Hat Virtualization environment must have at least one data storage domain, but adding more is recommended.

Warning

When installing or reinstalling the host’s operating system, Red Hat strongly recommends that you first detach any existing non-OS storage that is attached to the host to avoid accidental initialization of these disks, and with that, potential data loss.

A data domain holds the virtual hard disks and OVF files of all the virtual machines and templates in a data center, and cannot be shared across data centers while active (but can be migrated between data centers). Data domains of multiple storage types can be added to the same data center, provided they are all shared, rather than local, domains.

You can use one of the following storage types:

Prerequisites

  • Self-hosted engines must have an additional data domain with at least 74 GiB dedicated to the Manager virtual machine. The self-hosted engine installer creates this domain. Prepare the storage for this domain before installation.

    Warning

    Extending or otherwise changing the self-hosted engine storage domain after deployment of the self-hosted engine is not supported. Any such change might prevent the self-hosted engine from booting.

  • When using a block storage domain, either FCP or iSCSI, a single target LUN is the only supported setup for a self-hosted engine.
  • If you use iSCSI storage, the self-hosted engine storage domain must use a dedicated iSCSI target. Any additional storage domains must use a different iSCSI target.
  • It is strongly recommended to create additional data storage domains in the same data center as the self-hosted engine storage domain. If you deploy the self-hosted engine in a data center with only one active data storage domain, and that storage domain is corrupted, you cannot add new storage domains or remove the corrupted storage domain. You must redeploy the self-hosted engine.

3.1. Preparing NFS Storage

Set up NFS shares on your file storage or remote server to serve as storage domains on Red Hat Enterprise Virtualization Host systems. After exporting the shares on the remote storage and configuring them in the Red Hat Virtualization Manager, the shares will be automatically imported on the Red Hat Virtualization hosts.

For information on setting up, configuring, mounting and exporting NFS, see Managing file systems for Red Hat Enterprise Linux 8.

Specific system user accounts and system user groups are required by Red Hat Virtualization so the Manager can store data in the storage domains represented by the exported directories. The following procedure sets the permissions for one directory. You must repeat the chown and chmod steps for all of the directories you intend to use as storage domains in Red Hat Virtualization.

Prerequisites

  1. Install the NFS utils package.

    # dnf install nfs-utils -y
  2. To check the enabled versions:

    # cat /proc/fs/nfsd/versions
  3. Enable the following services:

    # systemctl enable nfs-server
    # systemctl enable rpcbind

Procedure

  1. Create the group kvm:

    # groupadd kvm -g 36
  2. Create the user vdsm in the group kvm:

    # useradd vdsm -u 36 -g kvm
  3. Create the storage directory and modify the access rights.

    # mkdir /storage
    # chmod 0755 /storage
    # chown 36:36 /storage/
  4. Add the storage directory to /etc/exports with the relevant permissions.

    # vi /etc/exports
    # cat /etc/exports
     /storage *(rw)
  5. Restart the following services:

    # systemctl restart rpcbind
    # systemctl restart nfs-server
  6. To see which export are available for a specific IP address:

    # exportfs
     /nfs_server/srv
                   10.46.11.3/24
     /nfs_server       <world>
Note

If changes in /etc/exports have been made after starting the services, the exportfs -ra command can be used to reload the changes. After performing all the above stages, the exports directory should be ready and can be tested on a different host to check that it is usable.

3.2. Preparing iSCSI Storage

Red Hat Virtualization supports iSCSI storage, which is a storage domain created from a volume group made up of LUNs. Volume groups and LUNs cannot be attached to more than one storage domain at a time.

For information on setting up and configuring iSCSI storage, see Getting started with iSCSI in Managing storage devices for Red Hat Enterprise Linux 8.

Important

If you are using block storage and intend to deploy virtual machines on raw devices or direct LUNs and manage them with the Logical Volume Manager (LVM), you must create a filter to hide guest logical volumes. This will prevent guest logical volumes from being activated when the host is booted, a situation that could lead to stale logical volumes and cause data corruption. Use the vdsm-tool config-lvm-filter command to create filters for the LVM. See Creating an LVM filter

Important

Red Hat Virtualization currently does not support block storage with a block size of 4K. You must configure block storage in legacy (512b block) mode.

Important

If your host is booting from SAN storage and loses connectivity to the storage, the storage file systems become read-only and remain in this state after connectivity is restored.

To prevent this situation, add a drop-in multipath configuration file on the root file system of the SAN for the boot LUN to ensure that it is queued when there is a connection:

# cat /etc/multipath/conf.d/host.conf
multipaths {
    multipath {
        wwid boot_LUN_wwid
        no_path_retry queue
    }

3.3. Preparing FCP Storage

Red Hat Virtualization supports SAN storage by creating a storage domain from a volume group made of pre-existing LUNs. Neither volume groups nor LUNs can be attached to more than one storage domain at a time.

Red Hat Virtualization system administrators need a working knowledge of Storage Area Networks (SAN) concepts. SAN usually uses Fibre Channel Protocol (FCP) for traffic between hosts and shared external storage. For this reason, SAN may occasionally be referred to as FCP storage.

For information on setting up and configuring FCP or multipathing on Red Hat Enterprise Linux, see the Storage Administration Guide and DM Multipath Guide.

Important

If you are using block storage and intend to deploy virtual machines on raw devices or direct LUNs and manage them with the Logical Volume Manager (LVM), you must create a filter to hide guest logical volumes. This will prevent guest logical volumes from being activated when the host is booted, a situation that could lead to stale logical volumes and cause data corruption. Use the vdsm-tool config-lvm-filter command to create filters for the LVM. See Creating an LVM filter

Important

Red Hat Virtualization currently does not support block storage with a block size of 4K. You must configure block storage in legacy (512b block) mode.

Important

If your host is booting from SAN storage and loses connectivity to the storage, the storage file systems become read-only and remain in this state after connectivity is restored.

To prevent this situation, add a drop-in multipath configuration file on the root file system of the SAN for the boot LUN to ensure that it is queued when there is a connection:

# cat /etc/multipath/conf.d/host.conf
multipaths {
    multipath {
        wwid boot_LUN_wwid
        no_path_retry queue
    }

3.4. Preparing Red Hat Gluster Storage

For information on setting up and configuring Red Hat Gluster Storage, see the Red Hat Gluster Storage Installation Guide.

For the Red Hat Gluster Storage versions that are supported with Red Hat Virtualization, see https://access.redhat.com/articles/2356261.

3.5. Customizing Multipath Configurations for SAN Vendors

If your RHV environment is configured to use multipath connections with SANs, you can customize the multipath configuration settings to meet requirements specified by your storage vendor. These customizations can override both the default settings and settings that are specified in /etc/multipath.conf.

To override the multipath settings, do not customize /etc/multipath.conf. Because VDSM owns /etc/multipath.conf, installing or upgrading VDSM or Red Hat Virtualization can overwrite this file including any customizations it contains. This overwriting can cause severe storage failures.

Instead, you create a file in the /etc/multipath/conf.d/user.conf directory that contains the settings you want to customize or override.

VDSM executes the files in /etc/multipath/conf.d/user.conf in alphabetical order. So, to control the order of execution, you begin the filename with a number that makes it come last. For example, /etc/multipath/conf.d/user.conf/90-myfile.conf.

To avoid causing severe storage failures, follow these guidelines:

Warning

Not following these guidelines can cause catastrophic storage errors.

Prerequisites

  • VDSM is configured to use the multipath module. To verify this, enter:

    # vdsm-tool is-configured --module multipath

Procedure

  1. Create a new configuration file in the /etc/multipath/conf.d/user.conf directory.
  2. Copy the individual setting you want to override from /etc/multipath.conf to the new configuration file in /etc/multipath/conf.d/user.conf. Remove any comment marks, edit the setting values, and save your changes.
  3. Apply the new configuration settings by entering:

    # systemctl reload multipathd
    Note

    Do not restart the multipathd service. Doing so generates errors in the VDSM logs.

Verification steps

Test the new configuration performs as expected on a non-production cluster in a variety of failure scenarios. For example, disable all of the storage connections. Then enable one connection at a time and verify that doing so makes the storage domain reachable.