[Lustre-discuss] Limit of OSTs per OSS?

[Sébastien Buisson]

Hi,

Just a small feedback from our own experience.
I agree with Brian about the fact that there is no strong limit on the 
number of OSTs per OSS in the Lustre code. But one should really take 
into account the available memory on OSSes when defining the number of 
OSTs per OSS (and so the size of each OST). If you do not have 1GB or 
1.2 GB of memory per OST on your OSSes, you will run into serious 
trouble with "out of memory" messages.

For instance, if you want 8 OSTs per OSS, your OSSes should have at 
least 10GB of RAM.

Unfortunately we experienced those "out of memory" problems, so I advise 
you to read Lustre Operations Manual chapter 33.12 "OSS RAM Size for a 
Single OST".

Cheers,
Sebastien.


Arne Wiebalck a écrit :
> Brian J. Murrell wrote:
>> On Wed, 2009-08-19 at 11:45 +0200, Arne Wiebalck wrote:
>>> is there a limit on the number of OSTs per OSS?
>>
>> I have never run across one so there is likely no *practical* limit.  I
>> could very well be corrected on this though.
>>
>> 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.
> 
> Thanks for the quick reply,
>  Arne
> 
> 
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