Error extending a striped LVM volume

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Environment

SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 12 Service Pack 1 (SLES 12 SP1)
SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 11 Service Pack 4 (SLES 11 SP4)
Logical Volume Management (LVM)

Situation

An existing stripped LVM volume has three stripes. Two additional disks were added to the parent volume group, and the logical volume extended using the lvextend command.

However, the logical volume was not extended as expected. Errors observed:

On SLE11

sles11sp4:~ # lvextend --extents +100%FREE /dev/data/vol1
  Using stripesize of last segment 64.00 KiB
  Rounding size (3323 extents) down to stripe boundary size for segment (3321 extents)
  Extending logical volume vol1 to 12.97 GiB
  Insufficient suitable allocatable extents for logical volume vol1: 1020 more required

On SLE12

sles12sp1:~ # lvextend --extents +100%FREE /dev/data/vol1
  Using stripesize of last segment 64.00 KiB
  Size of logical volume data/vol1 unchanged from 7.45 GiB (1908 extents).
  Logical volume vol1 successfully resized

NOTE: The SLE12 message suggests the volume has been resized, but the message also says the volume was "unchanged". A closer look shows the volume was not changed.

From the SLE11 example, the following shows available space in the volume group "data".

sles11sp4:~ # vgextend data /dev/sd[b-c]2
  Volume group "data" successfully extended

sles11sp4:~ # vgs
  VG   #PV #LV #SN Attr   VSize  VFree
  data   5   1   0 wz--n- 12.98g 3.99g

After the error, both SLE11 and SLE12 show similar output shown below. No additional segments are added as expected and the size of the logical volume is unchanged.

sles11sp4:~ # lvs --segments
  LV   VG   Attr      #Str Type    SSize
  vol1 data -wi-ao---    3 striped 8.99g

Resolution

Extend the volume group with equal multiples of the stripe count. In this case, the stripe count is three, so three disks must be added to extend the logical volume size. Only two had been added.

The following commands resolve the issue:

sles11sp4:~ # vgextend data /dev/sdd2
  Volume group "data" successfully extended

sles11sp4:~ # lvextend --extents +100%FREE /dev/data/vol1
  Using stripesize of last segment 64.00 KiB
  Extending logical volume vol1 to 14.98 GiB
  Logical volume vol1 successfully resized

sles11sp4:~ # lvs --segments
  LV   VG   Attr      #Str Type    SSize
  vol1 data -wi-ao---    3 striped 8.99g
  vol1 data -wi-ao---    3 striped 5.99g

Cause

The number of physical devices added to the volume group did not match the stripe count on the logical volume.

Disclaimer

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