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My /dev/md0 array just died last night. I got this email

This is an automatically generated mail message from mdadm running on

A Fail event had been detected on md device /dev/md0.

It could be related to component device /dev/sdb.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [raid6] [raid5] [raid4] md0 : active raid5 sdb0 sde[4] sdd[2] sdc1 4395411456 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/2] [__UU]

unused devices:

So, i had to pull the plug :(

After reboot, array failed to restart.

mdadm -A /dev/md0

mdadm: /dev/md0 assembled from 2 drives - not enough to start the array.

cat /proc/mdstat

Personalities : 
md0 : inactive sdd[2](S) sde[4](S) sdc[1](S) sdb[0](S)
      5860550240 blocks super 1.2

unused devices: <none>

and

mdadm --assemble --force --verbose /dev/md0 /dev/sdc /dev/sdb

mdadm: looking for devices for /dev/md0
mdadm: /dev/sdc is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdb is identified as a member of /dev/md0, slot 0.
mdadm: added /dev/sdc to /dev/md0 as 1
mdadm: no uptodate device for slot 2 of /dev/md0
mdadm: no uptodate device for slot 3 of /dev/md0
mdadm: added /dev/sdb to /dev/md0 as 0
mdadm: /dev/md0 assembled from 2 drives - not enough to start the array.

Ideas?

Thank you

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Why did you attempt to assemble with only two drives? – Paul Dec 29 '11 at 22:24
    
I'm pretty sure you can assemble with two drives, just enter "/dev/sdc /dev/sdb missing" – Sirex Dec 30 '11 at 8:56

RAID5 is not fault-tolerant of more than a single drive failure. You can try to re-add one or both of the dropped devices, but if they are not in a state to be re-added, then your data is quite possibly hosed (or at least needs advanced recovery).

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