Cluster Shared LVM Limitation

This document (000019652) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise High Availability Extension 15 SP1
SUSE Linux Enterprise High Availability Extension 12 SP4
SUSE Linux Enterprise High Availability Extension 12 SP5
SUSE Linux Enterprise Server 15 SP1
SUSE Linux Enterprise Server 12 SP4
SUSE Linux Enterprise Server 12 SP5

Situation

Is it possible to take snapshot for Logical Volume when LVM volumes are activated via shared cluster locking (clvm | lvmlockd)?

SLES12 --> clvm: Trying to create a snapshot on a LVM shared volume. ACTIVE|ACTIVE

lvcreate -L 1G -s -n test_snap /dev/clustervg/lnx_node1.vda.raw
  lnx_node1.vda.raw must be active exclusively to create snapshot

SLES15 --> lvmlockd: Trying to create a snapshot on a LVM shared volume will fail to get a lock.

lvcreate --size 200M --snapshot --name snap_shared vg-shared/lv-shared
  LV locked by other host: vg-shared/lv-shared
  Failed to lock origin LV vg-shared/lv-shared

Is it possible to resize Shared Logical Volume?

SLES15 --> lvmlockd: Trying to resize a Shared Logical Volume will fail:

lvextend -r -L +8M /dev/vgshared/lvshared 
  LV is already locked with incompatible mode: vgshared/lvshared

Resolution

This feature plus a few others are not supported on shared LVM volumes managed by clvm or lvmlockd.

Cause

LVM snapshot feature has never been supported by clvm or lvmlockd from the beginning.
Resizing Shared Logical Volume Is not supported/possible.

They are complex enough and can not be supported at this time.

Additional Information

man lvmlockd

LV activation
  sy     The command activates the LV in shared mode, allowing multiple hosts to activate the LV concurrently.  
     Before activating the LV, the command uses lvmlockd to acquire a shared lock on the LV.  
     If the lock cannot be acquired, the LV is not activated and an error is reported.  
     This would happen if the LV is active exclusively on another host.   
     If  the  LV  type prohibits shared access, such as a snapshot, the command will report an error and fail.  
     The shared mode is intended for a multi-host/cluster application or file system.  
     LV types that cannot be used concurrently from multiple hosts include thin, cache, raid, and snapshot.

[...]

  limitations of shared VGs
       Things that do not yet work in shared VGs:
       · using external origins for thin LVs
       · splitting snapshots from LVs
       · splitting mirrors in sanlock VGs
       · pvmove of entire PVs, or under LVs activated with shared locks
       · vgsplit and vgmerge (convert to a local VG to do this)

Note: Resizing Shared LVM should be possible starting from lvm2 v2.03.x in SLE15SP2.

Disclaimer

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Document ID:000019652
Creation Date: 14-Jul-2020
Modified Date:15-Jul-2020
- SUSE Linux Enterprise High Availability Extension
- SUSE Linux Enterprise Server

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