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

[Markus Krause <markus.krause@gmx.net>]

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Am Mon, 2002-11-25 um 10.59 schrieb Neil Brown: 
> 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
hi again and sorry for the delayed answer, i had to work a few days 
"on the road" and could not test your suggestion until some minutes ago!
and i worked exactly as you described! great! thanks a lot, thats real
cool! 

what i did exactly (maybe someone else is interested): 
(i snipped the output) 

  [root@merlin root]# mdadm -A /dev/md0 --force /dev/sda1 /dev/sdb1
/dev/sdc2

  [root@merlin root]# fsck.ext3 -n /dev/md0 

  [root@merlin root]# mdadm /dev/md0 -a /dev/sdc

and everything worked, all the data is back again!

well, except the fact, that now its a ext2 file system and not ext3, but
right now (till the current project is done in about two weeks) thats ok
for me, i can (must!) life without a journal file system.

thanks again for all your help!

   markus

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