[Lustre-devel] Fwd: Disk rebuild

[Andreas Dilger]

On 2009-12-02, at 13:58, Nikita Danilov wrote:
>> The problem lies in the way that obdfilter submits IO.  Since it is  
>> not
>> using the normal buffer cache to track "data=ordered" (or in the  
>> case of
>> this patch "data=declared") mode the bio_submit() will likely start
>> modifying the MD device before the corresponding declare blocks are
>> committed to the journal.
>
> Thank you for the detailed explanation, data-path completely escaped
> my mind. Still, on the mdt side, osd goes through the normal VFS paths
> and data=declared should work, right?

Yes, though in general the MDT is a lot smaller than the OSTs, fails  
less often, has RAID-1 instead of RAID-6 so the rebuild goes  
considerably faster, has metadata journaling for everything (so  
doesn't get inconsistent in the first place).

There would likely be some improvement, but we haven't benchmarked it  
- the main concern was for the OSTs.


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