[Lustre-discuss] recreate metada - possible?

[Andreas Dilger]

On Jul 15, 2009  08:32 -0400, Brian J. Murrell wrote:
> Even if it was completely wiped, the process of scanning the entire disk
> looking for "signatures" that can help identify a likely partition
> beginning and then recreate the partition table is usually quite
> successful.  You might want to look into the "gpart" tool for this.
> 
> On Wed, 2009-07-15 at 10:53 +0200, Tom Woezel wrote:
> > Now here is my question is, it possible to create a new MGS and new  
> > MDTs and somehow connect the old OSTs to them?
> 
> No.  There is nothing on the OSTs that indicate what file an object
> belongs to.  This is why we are adamant about MDT storage being reliable
> and backed up.

That isn't totally correct - there is an xattr on each OST object that
contains the MDT inode number and stripe index for that object.  That
doesn't help much in this case, because you will still have a whole
filesystem of objects without filenames.

> Without knowing the whole story of your MDT/RAID saga, I'd say gpart is
> your best bet.

Recovering the MDS data using gpart seems like a better idea.  If the
corruption is in the RAID layout itself, that is a harder issue to fix.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.