Mirko Benz wrote:
Hi,
We are testing 1.6 beta7 over IB. On a test setup (1 MDS, 1 OSS with 6
OSTs (RAID 5 each 5 drives)) we observer uneven load among the OSTs.
Testing from one to 5 clients Lustre schedules evenly (one OST per
client). With client count > 5 sometimes one OST is not used at all
(e.g. 6, 9 clients) or the utilisation is not as expected. The FS is
otherwise empty. We used IOR for testing.
There is never a 1:1 mapping between clients and OSTs. A round-robin
algorithm is used for OST stripe selection until the OST free space
differs by more than 20%. However, depending on how big the files
actually are, some stripes may be mostly empty and some full.
For a more complete explanation stripe assignments, see
http://arch.lustre.org/index.php?title=Feature_Free_Space_Management
The behavior can be reproduced. Uneven OST utilisation leads to lower
than possible performance. How can we achieve better distribution over
the OSTs without manual assignment?
Is there a setting to have a round-robin scheduling for the OST to use?
As explained above.
---
Stripe setting:
We want to have very high performance to a single client by striping
over 6 OSTs.
What parameters should be adjusted to achieve optimal performance?
Set the default stripe count to 6:
lctl> conf_param <fsname>-MDT0000.lov.stripecount=6
Thanks,
Mirko
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