[Lustre-discuss] Poor metadata operation performance

[Andreas Dilger]

It would be interesting to find out what is causing the bottleneck. At one time there was no throttle on the number of RPCs that the MDS could send, which caused overload problems on the OSTs. 

Now, the MDS is limited by the normal rpcs_in_flight tunable (=8) that clients are limited to. It would be worthwhile to see if increasing this helped the overall performance? If yes, then it would make sense to tune the OSCs on the MDS for more RPCs by default. 

Cheers, Andreas

On 2011-05-20, at 10:47 AM, Ken Hornstein <kenh at cmf.nrl.navy.mil> wrote:

>> Ken, the OSTs need to track the ownership of objects for quota.  The more
>> stripes there are on a file, the more RPCs that need to be sent, which is why
>> we don't recommend wide striping unless there is a reason for it (bandwidth,
>> size, etc).
> 
> Fair enough; I always forget about quota accounting, because we never use
> it.  But I'm wondering why this in particular causes such a hit, because
> the MDS sends the setattr RPCs asynchronously; in theory it should just
> fire them off and not have to wait until they're done.  Perhaps it's the
> overhead of sending those RPCs which is slowing things down?  I could believe
> that, although I would have thought that it wouldn't be that bad.
> 
> --Ken
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