[Lustre-discuss] Unbalanced OSTs
Andreas Dilger
adilger at sun.com
Thu Feb 18 13:47:58 PST 2010
On 2010-02-18, at 10:19, syed haider wrote:
> 1 combined MGS/MDT, 4 OSS's attached to DDN controller/SAN
> We have 32 1Tb OSTs (8 on each OSS) and because of the nature of our
> jobs, the files written to lustre vary greatly (5MB ~ 400GB size
> files).
> we have very high inconsistencies in disk space usage. One OST maybe
> only 40% full while another 94% full.
If your files are up to 40% of the OST size, then only 1 + fraction
files
are needed to hit a 50% imbalance between OSTs. I would really
suggest to
use 8TB OSTs to minimize this effect.
> The only solution I see is increasing each OST from 1TB to maybe 2
> or 3TB? So this lead me to my second question - what type of
> performance degradation (if any) am I looking at if increase the
> size of the OSTs? and is there a limit to the size of OSTs? Any
> input is appreciated!
Also, with the DDN it doesn't make any sense to split an 8TB tier of
disks into 8 separate 1TB LUNs. That is just causing extra contention
on the disks shared between these 8 LUNs, and hurting your
performance. Most DDN installations use the 8TB LUN size, which is
the maximum size until 1.8.2 where it goes to 16TB (enough for a tier
of 2TB disks).
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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