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Ultra 6 - X-RAID 2 (dual redundancy) volume not expanding
Hi, My ReadyNAS Ultra 6 X-RAID2 (with dual redundancy) configuration was: /dev/sda = 2TB /dev/sdb = 3TB /dev/sdc = 2TB /dev/sdd = 3TB /dev/sde = 4TB (3TB assigned) /dev/sdf = 3TB This c...
After unmounting volume c I've resized the physical volume /dev/md3 (since the RAID6 array has already been expended) and extendend the logical volume with 1.82T. After that I've resized the ext4 filesystem on /dev/c/c:
pvresize /dev/md3 lvextend -L +1.82T -n /dev/c/c /dev/md3 resize2fs -pf /dev/c/c
Now is everything as I expected it to be:
df -h Filesystem Size Used Avail Use% Mounted on /dev/md0 4.0G 1.4G 2.5G 37% / tmpfs 16K 0 16K 0% /USB /dev/c/c 11T 8.8T 2.1T 82% /c
Rebooting didn't solve my problem.
I've started with a capacity of 7.5TB, so the 8 TiB growth limit should not be a problem. The logs are not stating anything usefull, besides that it is trying to extend the logical volume by "0" bytes:
[2015/09/26 15:03:15 3419] LINE 4374: exec command: lvextend /dev/c/c -l +0 New size (148592 extents) matches existing size (148592 extents)
Since mdadm was showing that the partitions sda4 and sdc4 are not part of md3 (RAID 6), I'm now trying to add them manually:
mdadm --add /dev/md3 /dev/sda4 mdadm --add /dev/md3 /dev/sdc4 mdadm -v --grow --raid-devices=6 /dev/md3
Within 10 hours the restriping of md3 should be finished and hopefully I will be able to extend the logical volume after that.
cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md3 : active raid6 sdc4[5] sda4[4] sdb4[0] sde4[3] sdf4[2] sdd4[1]
1953501568 blocks super 1.2 level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
[=====>...............] reshape = 27.2% (265943836/976750784) finish=590.4min speed=20062K/sec
md2 : active raid6 sda3[7] sde3[5] sdf3[4] sdd3[3] sdc3[8] sdb3[6]
7795170816 blocks super 1.2 level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
md1 : active raid6 sda2[7] sde2[5] sdf2[4] sdd2[3] sdc2[8] sdb2[6]
2096896 blocks super 1.2 level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
md0 : active raid1 sda1[7] sde1[5] sdf1[4] sdd1[3] sdc1[8] sdb1[6]
4193268 blocks super 1.2 [6/6] [UUUUUU]
unused devices: <none>
After unmounting volume c I've resized the physical volume /dev/md3 (since the RAID6 array has already been expended) and extendend the logical volume with 1.82T. After that I've resized the ext4 filesystem on /dev/c/c:
pvresize /dev/md3 lvextend -L +1.82T -n /dev/c/c /dev/md3 resize2fs -pf /dev/c/c
Now is everything as I expected it to be:
df -h Filesystem Size Used Avail Use% Mounted on /dev/md0 4.0G 1.4G 2.5G 37% / tmpfs 16K 0 16K 0% /USB /dev/c/c 11T 8.8T 2.1T 82% /c
Is far as I know from answers around the internet, RAID 6 bij default needs at least 4 drives (of the same size, that is) to operate (which is strange as technically for dual reduncandy 3 should be enough). I guess if you added a 4th 4TB drive, it would have expanded as expected.
It's good to know one can manually override this behaviour.
RAID-6 does require a minimum of four disks.
The volume capacity now is the same as it would have been with 6x3TB disks. If another 4TB disk is added then offline volume expansion may be possible to expand it a further couple of TB.
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