How to configure LVM filters in RHV 4.1 and higher?

Solution Verified - Updated

Environment

  • Red Hat Virtualization 4.1, 4.2, 4.3, 4.4

Issue

  • How to configure LVM filters in RHV environment ?
  • How to use vdsm-tool for configuring lvm filters on hosts automatically on Red Hat Virtualization Hosts?

Resolution

Since RHV-4.1.9 (vdsm-4.19.44), a tool to configure the lvm filter on hosts automatically is available, as its automatic its less prone to errors compared to making changes manually in the /etc/lvm/lvm.conf.

Summary Steps:
For every host in the Data-Center:
1. Switch host to Maintenance Mode
2. SSH to host
3. If the boot device is a local disk, blacklist it in multipath [*]
4. Run the vdsm-tool config-lvm-filter tool
5. Reboot host
6. Activate host

Below is the example to use the tool: 

# /usr/bin/vdsm-tool config-lvm-filter
Analyzing host...
Found these mounted logical volumes on this host:

  logical volume:  /dev/mapper/rhvh_dhcp209--193-home
  mountpoint:      /home
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-rhvh--4.1--0.20180126.0+1
  mountpoint:      /
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-swap
  mountpoint:      [SWAP]
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-tmp
  mountpoint:      /tmp
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-var
  mountpoint:      /var
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-var_log
  mountpoint:      /var/log
  devices:         /dev/vda2

  logical volume:  /dev/mapper/rhvh_dhcp209--193-var_log_audit
  mountpoint:      /var/log/audit
  devices:         /dev/vda2

This is the recommended LVM filter for this host:

  filter = [ "a|^/dev/vda2$|", "r|.*|" ]

This filter will allow LVM to access the local devices used by the
hypervisor, but not shared storage owned by Vdsm. If you add a new
device to the volume group, you will need to edit the filter manually.

Configure LVM filter? [yes,NO] yes
Configuration completed successfully!

Please reboot to verify the LVM configuration.

As /dev/vda is a local disk it is also recommended to ignore it in multipath. Please follow the Documentation - Ignoring Local Disks when Generating Multipath Devices on how to ignore the local disk using the WWID of the device. For example:

# mkdir /etc/multipath/conf.d
# vi /etc/multipath/conf.d/blacklist.conf

blacklist {
      wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
}

[*] Why it is important to blacklist the local device in mutlipath?
If not configured, in the next boot/upgrade, multipath will take over the device before lvm, lvm would not find it and the machine would fail to boot. For details, see RHV host boot into emergency mode after upgrade .

NOTE: It is not recommended to configure a global_filter in /etc/lvm/lvm.conf, as this could prevent VDSM from seeing block-based storage domains.

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