What is lvmetad and how do I disable it?

Solution Verified - Updated 2 Aug 2024

Environment

Red Hat Enterprise Linux 9
Red Hat Enterprise Linux 8
Red Hat Enterprise Linux 7
Red Hat Enterprise Linux 6
LVM

Exceptions:

For RHEL8 hosts:

The `lvmetad` daemon does not exist in RHEL8. Starting in RHEL8, the lvm metadata is no longer read from cache, but from the disks directly.^[FN.4]

For Hosts within a Cluster:

If the host is a member of a cluster, then review the following before disabling lvmetad: "Why I got warning "WARNING: Disable lvmetad in lvm.conf lvmetad should never be enabled in a clustered environment." from messages log ?"^[FN.3]

Issue

What is lvmetad and its function? ^[FN.1]
The lvmetad daemon is enabled by default, and I need to disable lvmetad ^[FN.2]

May be seeing issues at boot up when lvmetad is enabled

Warning: /dev/mapper/rootvg-lv_root does not exist
Warning: /dev/rootvg/lv_root does not exist

LVM changes are not reflected by the rest of the nodes in my cluster.
After creating a volume group on a node in my cluster the other nodes do not reflect the change.

Resolution

To disable^[FN.2] the use of lvmetad^[FN.1] you will need to make the following changes:

Check current feature and service status
Disable feature at boot time vis use_lvmetad=0 ^{[FN.4],[FN.5]}
Disable run-time service(s) using sytemctl
Verify changes
Rebuild boot image file to reflect above changes (optional) ^[FN.1]
Reboot (optional)

Check lvmetad current status:

 grep use_lvmetad /etc/lvm/lvm.conf | xargs -I {} echo {} | grep -v "^#"
 systemctl status lvm2-lvmetad                                             # RHEL 8+ only

Disable lvmetad feature: ensure the use_lvmetad value in the /etc/lvm/lvm.conf file is set to 0 (off).
```
 use_lvmetad = 0
```

Disable lvmetad services: We will also need to disable the currently running lvmetad service

RHEL 8, 9:

  no actions required, lvmetad is not present in RHEL 8+

RHEL 7:

  # systemctl stop    lvm2-lvmetad
  # systemctl disable lvm2-lvmetad
  # systemctl stop lvm2-lvmetad.socket
  # systemctl disable lvm2-lvmetad.socket
  # systemctl mask lvm2-lvmetad.socket

RHEL 6

  # service lvm2-lvmetad stop
  # chkconfig lvm2-lvmetad off

Rebuild boot image to pick up changes: After making changes to the /etc/lvm/lvm.conf file, we will need to rebuild the initramfs to ensure the LVM configuration is loaded properly at next boot time. More information is available here: "How to rebuild the initial ramdisk image in Red Hat Enterprise Linux".
```
 # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak
 # dracut -f -v
```
Reboot (optional): Optionally you may wish to reboot to validate the above changes are applied as expected.

Same issue persists after above

If same issue then collect the below data from the system (for example in maintence mode if the system will not complete boot successfully).

  # cat /etc/fstab > /tmp/fstab.out
  # lsblk > /tmp/lsblk.out
  # df -h > df.out
  # cat /proc/mounts > /tmp/proc-mounts.out
  # journalctl -xb > /tmp/journactl.out

Compress the collected files.

  # tar -cJf  /tmp/CASENUMBER_lvmdiags.tar.xz /tmp/*out

Provide the above file and reference to this document to an existing or newly opened Red Hat support case.
- "Contacting Red Hat Technical Support"

Footnotes

Why you should not disable the lvmetad feature long term.

What is lvmetad, and what is it's function?

Additional resources for LVM in a cluster/high availability environment:
- Support Policies for RHEL High Availability Clusters - LVM in a Cluster"

The lvmetad daemon does not exist in RHEL8 so does not, and cannot, be disabled -- it is already implicitly disabled. What replaced it?
```
#  systemctl status lvm2-lvmetad
Unit lvm2-lvmetad.service could not be found.
```

Disabling just the service (systemctl) is not enough to guarantee disabling the feature.
You must disable the lvmetad feature, not just the service. If just the lvmetad service is disabled (the feature is not disabled), then lvmetad service can, and often will, end up resulting in the lvmetad> getting auto restarted. The feature must be first disabled via the lvmetad=0 configuration clause within the /etc/lvm/lvm.conf lvm configuration file.

For a complete rebuild of the lvm cache data utilized by lvmetad, it is recommended that the following commands be run:

# pvscan
# vgscan              # especially important if the lvm.conf:filter settings have been changed
# lvscan

LVM filtering notes.
- The lvm configuration file /etc/lvm/lvm.conf has two filter key:value pairs:
  - fliter= ; used for filtering devices when command are run and
  - global_filter=; used for event driven auto activication (e.g. systemd+udev in RHEL 7+)
- What is LVM's filter setting and how do I configure it easily in RHEL?
- How do I setup multipath on a system that already has LVM configured?
- Why do I see 'Found duplicate PV' warnings when using LVM with multipath storage in RHEL?

Root Cause

When set to 1 and when lvmetad is running (it is not auto-started), the volume group metadata and PV state flags are obtained from the lvmetad instance and no scanning is done by the individual commands. In a setup with lvmetad, lvmetad udev rules must be set up for LVM to work correctly. Without proper udev rules, all changes in block device configuration will be ignored until a manual pvscan --cache is performed.
See also the following references:

SBR

Product(s)

Red Hat Enterprise Linux

Components

lvm2

Category

Configure

Tags

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