[Lustre-discuss] recovering formatted OST

[Bernd Schubert]

On Friday, October 22, 2010, Andreas Dilger wrote:
> On 2010-10-22, at 12:25, Wojciech Turek wrote:
> > Actually I remember now, Andreas wrote some time ago that when one adds
> > OST in to the same slot as the old one MDS will think that the OST have
> > objects up to the what old OST had, and when the new OST starts it will
> > recreate those objects which may use a lot of inodes and space. So loop
> > device or ramdisk maybe not enough for that?
> 
> The ll_recover_lost_found_objs will at least recreate the O/0/LAST_ID file
> with the highest-available object ID, but given the corruption of the
> filesystem this may not cover all of the objects previously created.  I
> would suggest to read the last_id for this OST from the MDS:
> 
> mds> lctl get_param osc.*.prealloc_last_id
> 
> and then use a binary editor to set the LAST_ID on the recovered OST, if it
> is significantly different.


Hmm, if you remember, I have in my last_id patch a "TODO: new tool"?. What 
about simply manually creating an empty file on the OST with that ID (in the 
right obj-id % 32) directory and then let e2fsck do the job (I guess our DDN 
e2fsck is the only one which can do that so far).


Cheers,
Bernd