Re: Recovery/Access of imsm raid via mdadm?

[Dan Williams <djbw@fb.com>]

On Thu, Jan 10, 2013 at 12:19 PM, chris <tknchris@gmail.com> wrote:
> Hi Dave,
>
> Thanks for the tip, this has gotten me further
>
> # mdadm --assemble --scan
> # cat /proc/mdstat
> Personalities :
> md127 : inactive sdd[1](S) sdb[0](S)
>       4520 blocks super external:imsm
>
> So atleast now it has created an array of sorts but it only has 2 out
> of the 4 disks it should and also all disks appear to be marked as
> spares.
>
> Would I follow the same logic as typical mdadm recovery where I need
> to create the array again with the right layout and disks in right
> order and gain access to data without wiping it ?
>
> Any advice what direction to go in from here?
>

Backup the disks you have if possible.

Don't recreate the array with all 4 disks be sure to specify a missing
slot.  With mdadm-3.2.5 you do have support for creating imsm arrays
with 'missing' slots [1].  Then you can test some recreations to see
if you can find data.

At a minimum you know that sdb and sdd are in slot 2, 3, so the
question is finding a good candidate for slot 0, or 1.  It's a bit
concerning that the superblocks for those have been lost, or those
disks weren't moved over?  You can look for serial numbers in
/dev/disks/by-id.

--
Dan

[1]: http://marc.info/?l=linux-raid&m=131432484118038&w=2