Hypervisor LVM Configuration

Overview

PCD compute nodes (hypervisors) have LVM configured and running on the hypervisor node, must follow the guidelines below to properly configure LVM filters to prevent system hangs and performance issues.

This document outlines the required LVM filter configuration.

Check if LVM Package is Installed

Run the following command to check if LVM package is installed on your system.

dpkg -l | grep lvm
ii  libllvm15:amd64                        1:15.0.7-0ubuntu0.22.04.3               amd64        Modular compiler and toolchain technologies, runtime library
ii  liblvm2cmd2.03:amd64                   2.03.11-2.1ubuntu4                      amd64        LVM2 command library
ii  lvm2                                   2.03.11-2.1ubuntu5                      amd64        Linux Logical Volume Manager

If LVM is installed, you will see output similar to above. In that case, follow the steps below to set LVM filters.

Identify Physical Disk Devices On Your System

Run the command below to identify all the block devices mounted on this host. NOTE however that this command will also list any VM disks as well.

lsblk -o NAME,SIZE,TYPE,MOUNTPOINT,VENDOR,MODEL | grep disk
sda                        1.7T disk                    HPE      LOGICAL VOLUME
sdb                        1.0T disk                    HPE      LOGICAL VOLUME
sdg                         49G disk                    3PARdata VV
sdk                         49G disk                    3PARdata VV
sdl                         49G disk                    3PARdata VV
sdm                         49G disk                    3PARdata VV

Identify from the output above the subset of entries that are the physical disks for your hypervisor host.

In this example, you would only pick sda and sdb. The other four devices are volumes attached to VMs running on this host.

Add Or Enable LVM Filters For All Disks

Edit /etc/lvm/lvm.conf and locate the devices section.

Then edit the filter and global_filter values and add the entries for the physical disks for your hypervisor host that you identified above.

Note that this is a regular expression, where 'a' stands for accepting the path and 'r' stands for rejecting the path in the syntax below.

This example

devices {
    filter = [ "a|^/dev/sda|", "a|^/dev/sdb|", "r|.*|" ]
    global_filter = [ "a|^/dev/sda|", "a|^/dev/sdb|", "r|.*|" ]
}

Validate that the LVM Filters are Active

sudo lvm dumpconfig devices | grep -E "filter|global_filter"

Symptoms When Not Configured

If LVM is installed on your hypervisor but the LVM filters are not configured properly, here are some of the side effects and symptoms that you may observe on your Private Cloud Director hosts:

• QEMU processes stuck in uninterruptible sleep (D state)

• VM operations hang or timeout

• Slow system responsiveness on the host

• High I/O wait times during LVM operations

• VMs fail to start or become unresponsive