I have a storage box (currently under test) which has two 12-drive RAID6
arrays, /dev/md/data1 and /dev/md/data2.
The box crashed for an unrelated reason, and when I brought it back up, only
one of the arrays assembled:
root@storage1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md126 : active raid6 sdj[8] sdk[9] sdd[2] sde[3] sdi[7] sdm[11] sdg[5] sdc[1] sdb[0] sdl[10] sdh[6] sdf[4]
29302650880 blocks super 1.2 level 6, 1024k chunk, algorithm 2 [12/12] [UUUUUUUUUUUU]
md127 : inactive sdq[3](S) sdx[10](S) sdu[6](S) sdt[5](S) sds[4](S) sdv[8](S) sdp[2](S) sdy[11](S) sdo[1](S) sdn[0](S) sdw[9](S) sdr[7](S)
35163186720 blocks super 1.2
unused devices: <none>
So it looks like 12 of the disks have all become spares (S)!
An attempt to manually assemble the array failed:
root@storage1:~# mdadm --stop /dev/md127
mdadm: stopped /dev/md127
root@storage1:~# mdadm --assemble /dev/md/disk2 /dev/sd{n..y}
mdadm: /dev/md/disk2 assembled from 4 drives - not enough to start the array.
Since this is currently under test system I just forcibly recreated the
array, but I'm a bit worried about how I would handle this problem when I go
into production.
Here is how I recreated the array:
root@storage1:~# mdadm --create /dev/md/disk2 -n 12 -c 1024 -l raid6 /dev/sd{n..y}
mdadm: /dev/sdn appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdo appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdp appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdq appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdr appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sds appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdt appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdu appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdv appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdw appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdx appears to be part of a raid array:
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
mdadm: /dev/sdy appears to be part of a raid array:
# /etc/fstab: static file system information.
level=raid6 devices=12 ctime=Mon Mar 19 11:52:55 2012
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md/disk2 started.
So it seems like all the disks were known to be part of an array, but mdadm
was still unable to assemble more than 4.
Platform: Ubuntu 11.10 server x86_64, stock kernel:
Linux storage1 3.0.0-16-server #29-Ubuntu SMP Tue Feb 14 13:08:12 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Unfortunately I saw the same problem once before on a different test system,
and also had to forcibly rebuild the array.
So my questions are:
* Have I built the RAID array correctly in the first place? Are there some
options I could have given to mdadm to make it more robust?
* What should I have done when presented with an array which would not
assemble, to attempt to recover without losing data?
* Any ideas why mdadm only thought 4 of the drives were usable?
Thanks,
Brian.
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