Merging snapshot causing activation failure of origin volume after reboot

Solution Unverified - Updated -

Environment

  • Red Hat Enterprise Linux 5

Issue

  • Volume Group or Logical Volume activation fails with the following error
  Can't process LV LVNAME: snapshot-merge target support missing from kernel?
  0 logical volume(s) in volume group "VGNAME" now active
  • Logs show the following errors after activation attempt
kernel: device-mapper: table: 253:#: snapshot-merge: unknown target type
kernel: device-mapper: ioctl: error adding target to table

Resolution

1) Upgrade your lvm2 package to 2.02.88-11.el5 or greater

yum update lvm2

2) Re-active the volume

# vgchange -ay
Workaround

1) Identify a valid version of your LVM metadata by issuing the following grep command

# grep -l "\--merge" /etc/lvm/archive/*

2) Restore the metadata back to disk using the file in the output from the previous command

# vgcfgrestore -f /etc/lvm/archive/file.vg VGNAME

3) Rescan the Volume Group and reattempt the activation

# vgscan
# vgchange -ay VGNAME

Root Cause

  • The kernel in Red Hat Enterprise Linux 5 does not contain the logic to support snapshot merging

  • Support for snapshot merging in the kernel is only checked when the merge starts.

  • lvconvert does not check if the kernel supports merging when issuing the --merge option.

  • If the logical volume is not open at the time of the merge, the command will fail.

# lvconvert --merge VGNAME/LVSNAPNAME
  Can't process LV lv_origin: snapshot-merge target support missing from kernel?
  Failed to suspend origin LVNAME
  Unable to merge LV "LVSNAPNAME" into its origin.
  • If the logical volume is open at the time of the merge, the merge will occur during next activation, causing the issue.
# lvconvert --merge VGNAME/LVSNAPNAME
  Can't merge over open origin volume
  Merging of snapshot lv_snap will start next activation.

Diagnostic Steps

  • Check to see if activation fails agianst a volume after issuing merge command.
[root@rhel5 ~]# lvs vg_merge
  LV        VG       Attr   LSize   Origin    Snap%  Move Log Copy%  Convert
  lv_origin vg_merge owi-a- 500.00M                                         
  lv_snap   vg_merge swi-a- 100.00M lv_origin  64.54                        
[root@rhel5 ~]# mount /dev/vg_merge/lv_origin /mnt
[root@rhel5 ~]# lvconvert --merge vg_merge/lv_snap
  Can't merge over open origin volume
  Merging of snapshot lv_snap will start next activation.
[root@rhel5 ~]# lvs vg_merge
  LV        VG       Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  lv_origin vg_merge Owi-ao 500.00M                                      
[root@rhel5 ~]# umount /mnt
[root@rhel5 ~]# vgchange -an vg_merge
  0 logical volume(s) in volume group "vg_merge" now active
[root@rhel5 ~]# vgchange -ay vg_merge
  Can't process LV lv_origin: snapshot-merge target support missing from kernel?
  0 logical volume(s) in volume group "vg_merge" now active
[root@rhel5 ~]#
  • Check to see if merging is supported by looking for snapshot-merge in the output of the following command
# dmsetup targets
  • Check LV Attributes to see if the O attribute (snapshot merging with origin) has been set
# lvs VGNAME
  LV        VG       Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  LVNAME    VGNAME   Owi-ao 500.00M

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