Re: recover short-time-power-failure of raid 5?

On Monday November 25, krause@mogli-soft.de wrote:

hello neilbrown, 

thanks a lot for your fast response!
i tried the command as you suggested but i am not sure if it really
worked, it seems that /dev/sdc2 is not yet used (but of course i may be
wrong! ;-) )

.....

what about disk /dev/sdc2 ? i have tried to access /dev/sdc1 (a small
ext2 partition) and the data there was correct, so it seems that the
disk is accessable and did not got damaged by the shot power failure.

how can i get the third disk back into the raid system? or do i have to
backup all reconstructed data from the two disks and reinit the raid
from the start?

mdadm -A --force
will only 'force' into the array enough drives to make it work.  For
your 3 drive raid5 array, it ony needs to force in 2 drives, so it
takes the two most recent drives and uses them.  They will have all
the data on them, but no redundancy.

I suggest that after assembling the array, you 'fsck' the filesystem
on md0 just to make sure that the data is fine and then simply hot-add
the third device:
  mdadm /dev/md0 -a /dev/sdc

If fsck reports lots of error..... maybe try force the assmbly from a
different pair of drives. e.g.
   mdadm -A --force /dev/sda1 /dev/sdc2

and then do the fsck.

NeilBrown