[Lustre-discuss] recreate metada - possible?

[Robin Humble]

On Wed, Jul 15, 2009 at 08:32:27AM -0400, Brian J. Murrell wrote:
>On Wed, 2009-07-15 at 10:53 +0200, Tom Woezel wrote:
>> 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.

if a kernel is still up and looking at the device then /proc/partitions
and /sys/block/<disk>/* might well still contain enough valid data from
which the previous partition table can be reconstructed.

been there, dd'd over that. (almost) all good in the end :-)
thankfully not to a Lustre fs, just my home server :-/

cheers,
robin
--
Dr Robin Humble, HPC Systems Analyst, NCI National Facility

>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.
>



>_______________________________________________
>Lustre-discuss mailing list
>Lustre-discuss at lists.lustre.org
>http://lists.lustre.org/mailman/listinfo/lustre-discuss