Re: Help with recovering a RAID5 array

[Stefan Borggraefe <stefan@spybot.info>]

Am Freitag, 3. Mai 2013, 10:38:52 schrieben Sie:
> On Thu, May 2, 2013 at 2:24 PM, Stefan Borggraefe <stefan@spybot.info> 
wrote:
> > I am using a RAID5 software RAID on Ubuntu 12.04
> > 
> > It consits of 6 Hitachi drives with 4 TB and contains an ext 4 file
> > system.
> > 
> > When I returned to this server this morning, the array was in the
> > following
> > state:
> > 
> > md126 : active raid5 sdc1[7](S) sdh1[4] sdd1[3](F) sde1[0] sdg1[6] sdf1[2]
> > 
> >       19535086080 blocks super 1.2 level 5, 512k chunk, algorithm 2 [6/4]
> > 
> > [U_U_UU]
> > 
> > sdc is the newly added hard disk, but now also sdd failed. :( It would be
> > great if there was a way to have the this RAID5 working again. Perhaps
> > sdc1
> > can then be fully added to the array and after this drive sdd also
> > exchanged.
> I have had a few raid6 fail in a similar fashion: the 3rd drive
> faliing during rebuild (Also 4 TB Hitachi by the way).
> 
> I tested if the drives were fine:
> 
>   parallel dd if={} of=/dev/null bs=1000k ::: /dev/sd?
> 
> And they were all fine. 

Same for me.

> With only a few failing sectors (if any) I figured that very little
> would be lost by forcing the failing drive online. Remove the spare
> drive, and force the remaining online:
> 
>   mdadm -A --scan --force

I removed the spare /dev/sdc1 from /dev/md126

with

mdadm /dev/md126 --remove /dev/sdc1

After mdadm -A --scan --force the array is now in this state

md126 : active raid5 sdh1[4] sdd1[3](F) sde1[0] sdg1[6] sdf1[2]
      19535086080 blocks super 1.2 level 5, 512k chunk, algorithm 2 [6/4] 
[U_U_UU]
 
> Next step is to do fsck.

I think this is not possible yet at this point. Don't I need to reassemble the 
array using the --assume-clean option and with one missing drive first? Some 
step is missing here.

Stefan