[Lustre-discuss] recreate metada - possible?

[Brian J. Murrell]

On Wed, 2009-07-15 at 10:53 +0200, Tom Woezel wrote:
> Hi all,

Hi,

> I have a bit of a problem here. I am currently running Lustre 1.6.7 on  
> 5 servers. 2 servers for MGS/MDT and 3 for OSDs.

OST, not OSD.

> Behind the 2 MGS/MDT  
> servers (failover setup) is a raidarray so that both machines can use  
> the device.

Good.

> Now the partition table on the raiddevice got deleted and  
> cannot be recovered.

Ouch.  How did it get deleted?  How come it cannot be recovered?  A
partition table is nothing more than a small area at the start of a disk
that contains pointers (i.e. offsets on the disk) to where partitions
start and end.

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.

> The OSTs are ok and the data on those should be  
> fine.

Yes.  But all you have is file "contents", nothing else.

> 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.

> Is there a way to  
> recreate the metadata with the data whis is held on the OSTs?

No.

> I'm deeply grateful for any help or hint on this issue.

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

b.

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