I added a new drive to my RAID6 array, before I added the drive my array looked like this
$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid6 sde[5] sdc[1] sdb[6] sdf[4] sdd[3]
14650917888 blocks super 1.2 level 6, 512k chunk, algorithm 2 [5/5] [UUUUU]
bitmap: 1/37 pages [4KB], 65536KB chunk
unused devices: <none>
I then ran
$ sudo mdadm --add /dev/md0 /dev/sdg
$ sudo mdadm --grow /dev/md0 --level=6 --raid-devices=6 --backup-file=/root/raid6backup_mar2017
mdadm: Need to backup 6144K of critical section..
Afterwards my /proc/mdstat looked like this
Personalities : [raid6] [raid5] [raid4]
md0 : active raid6 sdg[7] sde[5] sdc[1] sdb[6] sdf[4] sdd[3]
14650917888 blocks super 1.2 level 6, 512k chunk, algorithm 2 [6/6] [UUUUUU]
[>....................] reshape = 0.0% (1/4883639296) finish=25435621.3min speed=0K/sec
bitmap: 0/37 pages [0KB], 65536KB chunk
unused devices: <none>
Which looks good on the face of it, but it says 0K/sec, and it looks like it has wrote nothing (1/4883639296) this is about my only hope that my data is still intact.
I did some googling for the problem, and I found this page Recover from raid-5 to raid-6 reshape and crash, mdadm reports 0K/sec rebuild and tried the answer it suggested, it seemingly had no effect. I mention it only for completeness.
Afterwards, I found this. https://serverfault.com/questions/833557/software-raid5-reshape-at-0k-sec-after-attempting-to-grow Looked promising, so I tried that, as soon as I ran the command, the machine locked up, stopped responding to SSH, the display was off and wouldn't turn back on again. So I resorted to powering off the machine.
I booted it back up again, and tried to rebuild the array.
$ sudo mdadm --assemble --backup-file=raid6backup_mar2017 /dev/md0 /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg
mdadm: Failed to restore critical section for reshape, sorry.
Hopefully someone can help me, I'm out of ideas at this point.
