help with recover data from software raid 1

Franz Waldmüller waldbauernbub at
Sun Aug 7 19:58:53 UTC 2011

Hi Jeffrey,

Am 2011-08-02 04:19, schrieb Jeffrey Gray:
> And as always, best practice would tell you that you should clone
> before anything.  Grab another drive of equal or larger LBA and bit
> for bit clone the drive.
Thank you for your advice. I have been offline this week due to an 
network error.
I purchased a spare drive and copied the content of the drives. Still I 
am trying to find out which drive is sdb and which sdc.
Is there somekind of UUID for disks?

> On Mon, Aug 1, 2011 at 8:59 PM, Luis Paulo<luis.barbas at>  wrote:
>> 2011/7/31 Franz Waldmüller<waldbauernbub 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
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