[Lustre-discuss] Limit of OSTs per OSS?

[Andreas Dilger]

On Aug 19, 2009  13:55 +0200, Arne Wiebalck wrote:
> Brian J. Murrell wrote:
>> On Wed, 2009-08-19 at 11:45 +0200, Arne Wiebalck wrote:
>> Unless you are making lots and lots of small OSTs -- which is not
>> usually beneficial anyway -- typically, you will run into resource
>> limitations (memory, bus bandwidth, etc.) on an OSS before you hit a
>> limit on the number of OSTs.
>
> I just thought I remembered there was something like 8 OSTs per OSS,
> but apparently I was wrong.
>
>> Just how many OSTs are you considering, and how big will they be?
>
> My OSSs will have 10 OSTs with 1TB each.

Is there a reason to do this instead of, say, two 5TB OSTs using MD RAID-0?
Or for that matter one 8+2 8TB OST with MD RAID-6?  That will give
better space utilization if you have large files, otherwise you will
have a lot of smaller chunks of free space on each OST that cannot
be utilized well when the OSTs are nearly full.

If you are looking at straight performance it may be that 10x 1TB OSTs
is the fastest, since each one can be seeked independently.  Reducing
the journal size from the default 400MB is probably not harmful if you
have correspondingly more OSTs.

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