help with recover data from software raid 1

[Luis Paulo]

2011/7/31 Franz Waldmüller <waldbauernbub at gmx.at>:
> Hi,
>
> I want to recover files from a disk which has been part of a raid1 array. I
> don't want to mount it degraded, as all operations must be read only.
>
> Can I mount the partiton of the disk as an ext4 filesystem (the raid was
> formatted as ext4.)?
>
> Background:
> In my server to harddisks are used in mirrored array to save all important
> data.
> /dev/sdb1 and /dev/sdc1
>
> today I created another md-device with the created partitions /dev/sdb2 and
> /dev/sdc2. Unfortunately I didn't edit the /etc/mdadm/mdadm.conf file
> properly.
> When I rebooted the server I checked /proc/mdstat
> and saw the following resync process:
>
> md1 : active raid1 sdc[1] sdb2[0]
>      391382976 blocks [2/2] [UU]
>      [>....................]  resync =  0.1% (745088/391382976)
>
> That is wrong, as the first device is sdc, but it should be sdc2.
> I halted the server and now have to recover the files from /dev/sdb1.
> /dev/sdc1 could have suffered damage from the resync process.
>
> I hope that you can help me with your advice.
>
> Franz


I don't understand why you don't want to assemble the array as degraded.

The way I'll recover the array will be clearing the super-block of
/dev/sdc1, assemble the array as degraded with dev/sdb1 and then add
/dev/sdc1 (using mdadm commands). At least this is the general idea, I
may (and you must before trying it) look more carefully into it.
After a resync, the array would be functional again.

Regards
Luis