Chapter 5. 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: NFS iSCSI Fibre Channel (FCP) POSIX-compliant file system Local storage Red Hat Gluster Storage 5.1. 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 Install the NFS utils package. # dnf install nfs-utils -y To check the enabled versions: # cat /proc/fs/nfsd/versions Enable the following services: # systemctl enable nfs-server # systemctl enable rpcbind Procedure Create the group kvm : # groupadd kvm -g 36 Create the user vdsm in the group kvm : # useradd vdsm -u 36 -g kvm Create the storage directory and modify the access rights. Add the storage directory to /etc/exports with the relevant permissions. # vi /etc/exports # cat /etc/exports /storage *(rw) Restart the following services: # systemctl restart rpcbind # systemctl restart nfs-server 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. 5.2. 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 Configuring an iSCSI target 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 } 5.3. 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 } } 5.4. Preparing POSIX-compliant File System Storage POSIX file system support allows you to mount file systems using the same mount options that you would normally use when mounting them manually from the command line. This functionality is intended to allow access to storage not exposed using NFS, iSCSI, or FCP. Any POSIX-compliant file system used as a storage domain in Red Hat Virtualization must be a clustered file system, such as Global File System 2 (GFS2), and must support sparse files and direct I/O. The Common Internet File System (CIFS), for example, does not support direct I/O, making it incompatible with Red Hat Virtualization. For information on setting up and configuring POSIX-compliant file system storage, see Red Hat Enterprise Linux Global File System 2 . Important Do not mount NFS storage by creating a POSIX-compliant file system storage domain. Always create an NFS storage domain instead. 5.5. Preparing local storage On Red Hat Virtualization Host (RHVH), local storage should always be defined on a file system that is separate from / (root). Use a separate logical volume or disk, to prevent possible loss of data during upgrades. Procedure for Red Hat Enterprise Linux hosts On the host, create the directory to be used for the local storage: # mkdir -p /data/images Ensure that the directory has permissions allowing read/write access to the vdsm user (UID 36) and kvm group (GID 36): # chown 36:36 /data /data/images # chmod 0755 /data /data/images Procedure for Red Hat Virtualization Hosts Create the local storage on a logical volume: Create a local storage directory: # mkdir /data # lvcreate -L USDSIZE rhvh -n data # mkfs.ext4 /dev/mapper/rhvh-data # echo "/dev/mapper/rhvh-data /data ext4 defaults,discard 1 2" >> /etc/fstab # mount /data Mount the new local storage: # mount -a Ensure that the directory has permissions allowing read/write access to the vdsm user (UID 36) and kvm group (GID 36): # chown 36:36 /data /rhvh-data # chmod 0755 /data /rhvh-data 5.6. 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 Red Hat Gluster Storage Version Compatibility and Support . 5.7. 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 directory that contains the settings you want to customize or override. VDSM executes the files in /etc/multipath/conf.d 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/90-myfile.conf . To avoid causing severe storage failures, follow these guidelines: Do not modify /etc/multipath.conf . If the file contains user modifications, and the file is overwritten, it can cause unexpected storage problems. Do not override the user_friendly_names and find_multipaths settings. For details, see Recommended Settings for Multipath.conf . Avoid overriding the no_path_retry and polling_interval settings unless a storage vendor specifically requires you to do so. For details, see Recommended Settings for Multipath.conf . Warning Not following these guidelines can cause catastrophic storage errors. Prerequisites VDSM is configured to use the multipath module. To verify this, enter: Procedure Create a new configuration file in the /etc/multipath/conf.d directory. Copy the individual setting you want to override from /etc/multipath.conf to the new configuration file in /etc/multipath/conf.d/<my_device>.conf . Remove any comment marks, edit the setting values, and save your changes. Apply the new configuration settings by entering: Note Do not restart the multipathd service. Doing so generates errors in the VDSM logs. Verification steps Test that 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. Enable one connection at a time and verify that doing so makes the storage domain reachable. Additional resources Recommended Settings for Multipath.conf Red Hat Enterprise Linux DM Multipath Configuring iSCSI Multipathing How do I customize /etc/multipath.conf on my RHVH hypervisors? What values must not change and why? 5.8. Recommended Settings for Multipath.conf Do not override the following settings: user_friendly_names no Device names must be consistent across all hypervisors. For example, /dev/mapper/{WWID} . The default value of this setting, no , prevents the assignment of arbitrary and inconsistent device names such as /dev/mapper/mpath{N} on various hypervisors, which can lead to unpredictable system behavior. Warning Do not change this setting to user_friendly_names yes . User-friendly names are likely to cause unpredictable system behavior or failures, and are not supported. find_multipaths no This setting controls whether RHVH tries to access devices through multipath only if more than one path is available. The current value, no , allows RHV to access devices through multipath even if only one path is available. Warning Do not override this setting. Avoid overriding the following settings unless required by the storage system vendor: no_path_retry 4 This setting controls the number of polling attempts to retry when no paths are available. Before RHV version 4.2, the value of no_path_retry was fail because QEMU had trouble with the I/O queuing when no paths were available. The fail value made it fail quickly and paused the virtual machine. RHV version 4.2 changed this value to 4 so when multipathd detects the last path has failed, it checks all of the paths four more times. Assuming the default 5-second polling interval, checking the paths takes 20 seconds. If no path is up, multipathd tells the kernel to stop queuing and fails all outstanding and future I/O until a path is restored. When a path is restored, the 20-second delay is reset for the time all paths fail. For more details, see the commit that changed this setting . polling_interval 5 This setting determines the number of seconds between polling attempts to detect whether a path is open or has failed. Unless the vendor provides a clear reason for increasing the value, keep the VDSM-generated default so the system responds to path failures sooner.

Commands:
dnf install nfs-utils -y
cat /proc/fs/nfsd/versions
systemctl enable nfs-server systemctl enable rpcbind
groupadd kvm -g 36
useradd vdsm -u 36 -g kvm
mkdir /storage chmod 0755 /storage chown 36:36 /storage/
vi /etc/exports cat /etc/exports /storage *(rw)
systemctl restart rpcbind systemctl restart nfs-server
exportfs /nfs_server/srv 10.46.11.3/24 /nfs_server <world>
cat /etc/multipath/conf.d/host.conf multipaths { multipath { wwid boot_LUN_wwid no_path_retry queue }
cat /etc/multipath/conf.d/host.conf multipaths { multipath { wwid boot_LUN_wwid no_path_retry queue } }
mkdir -p /data/images
chown 36:36 /data /data/images chmod 0755 /data /data/images
mkdir /data lvcreate -L USDSIZE rhvh -n data mkfs.ext4 /dev/mapper/rhvh-data echo "/dev/mapper/rhvh-data /data ext4 defaults,discard 1 2" >> /etc/fstab mount /data
mount -a
chown 36:36 /data /rhvh-data chmod 0755 /data /rhvh-data
vdsm-tool is-configured --module multipath
systemctl reload multipathd