[Lustre-discuss] recreate metada - possible?

[Tom Woezel]

Thank you all for the answers so far. The main problem with the raid  
is that the partition table has been overwritten. I don't know how it  
happened but it seems that another machine could see the raid device  
during a kickstart installation and used it (some of our kickstart  
files use the clearpart --all --initlabel option).

However I was able to recover a partition table with gpart (tried  
TestDisk befor and didn't work) and will now see if I can somehow  
recover the MGS and MDTs.

Regards
Tom

Am 15.07.2009 um 15:53 schrieb 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.
>
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