[Lustre-discuss] Unbalanced OSTs

[syed haider]

Thank you Andreas, you've answered my question. 4 OST's sounds a lot better
than 32!

On Thu, Feb 18, 2010 at 4:47 PM, Andreas Dilger <adilger at sun.com> wrote:

> 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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