Not being able to recover a RAID 5 20 Tb partition, help needed

[Roger Willcocks]

On Wed, 2014-01-29 at 14:39 +0100, Juan A. Sillero wrote:
> Hello,
> 
> We are a pioneering group in turbulence at the Polytechnic University of
> Madrid (torroja.dmt.upm.es), running simulations in supercomputing
> centers all around the world and hosting massive data in our data center
> that are publicly accessible.
> 
> Apparently we have lost one of our partitions of 20 Tb because of a
> under-voltage error of a power source plus a disk failure and we are
> trying to fix it, but it does not look good so far.
> 
> The system is setup as follow:
>         XFS 6.1
>         Raid 5 (12 x 2 disks of 2 Tb each)
>         Double disk controller managed by devmapper.
> 
> What we know at this point is the next:
> 
> 1) The topology of the disk is lost: the main-boot-record and the GPT
> are corrupted. 


Are you sure the array had a main-boot-record and GPT ? What makes you
think they are corrupted ?

> 2) After running the testdisk utility we find 9 partitions instead of 1.

There is a good chance that the discovered partitions are backup XFS
superblocks; their location and content may allow you to figure out the
array topology.


> 3) With gdisk we have tried to create a new main-boot-record and GPT,
> but it has not worked. 

This was a bad idea. Do you have a copy of the original data for these
sectors ?

> 4) We know that the blocksize is 4096 bytes, and the current capacity of
> the raid is under 20 Tb, so we suspect that even if the disk-manager
> says that the RAID is ok, it has not reconstructed the RAID after the
> disk failing.
> 
> We are stuck right now at this point, and help would be really
> appreciated in order to bring up the partition. We will be pleased to
> acknowledge the group in the upcoming publications.
> 
> Thanks again, Juan A. Sillero 

> 
-- 
Roger Willcocks <roger at filmlight.ltd.uk>