Help recovering a RAID set

Rashkae ubuntu at tigershaunt.com
Thu May 10 20:56:32 UTC 2012


On 05/10/2012 03:47 PM, Liam Proven wrote:
> The RAID in one of my servers died. Sadly, so did the disk with the
> backup on it when I tried to recover it. As did the disk in my desktop
> with another backup of all the important files.
>
> So, I am trying to recover the data.
>
> I used gddrescue to get image copies of the 4 × 40GB drives; they are
> on a 300GB drive, as partitions sdb5, sdb6, sdb7 and sdb8.
>
> I am trying to assemble them with mdadm but it reports that there's no
> superblock on any of them.
>
> Looking at the raw partitions with a hex editor, I can see that there
> are large slices of empty space at the start of each drive.
>
> On sdb5 and sdb6, the data starts at 0xB0000. On sdb7 and sdb8 it
> starts at 0xAA000.
>
> Can anyone suggest how I can prune off the first  720896 bytes of the
> first 2 partitions and the first 696320 bytes of the second 2?
>
> I have other spare drives - I could in principle `dd` the whole
> partitions onto other media, but I am not fluent enough in dd to skip
> the first $number blocks...
>

The version of mdadm that your array was created on probably used the 
superblocks that are store at the end of the device, not the start.  If 
these new paritions aren't exactly the same size as the original hard 
drives (or partitions therefof), that's why mdadm can't find the 
superblocks.   I've never recovered a raid array from such a situation, 
but I would think the best thing to do would be the dump the partitions 
from the original drives into a file rather than a new partition.






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