[Lustre-discuss] root on lustre and timeouts

[Robin Humble]

On Thu, Apr 30, 2009 at 12:51:00PM -0400, Brian J. Murrell wrote:
>On Thu, 2009-04-30 at 11:48 -0400, Robin Humble wrote:
>> BTW, as was pointed out in one talk of this years LUG, Lustre 1.8's
>> OSS read cache should help things like root-on-Lustre because small
>> commonly used files will likely be cached in the OSS's and won't result
>> in disk accesses.
>Yes, imagine what the ROSS cache can do for 150 clients all booting (and
>executing the same scripts/binaries) at the same time.  Imagine what the
>OSS disk did/does before the cache.  :-)

hopefully most of the frequently used parts of the OS are in page cache
on clients after the first read or two, but if there are new parts
accessed (or if everything boots at once) then yes, the OSS read cache
should definitely help lots.  

currently the only load we notice from root-on-Lustre is on the MDS,
but I can't say we've been actively monitoring and categorising all the
traffic - we really haven't felt the need because there haven't been
slowdowns to speak of - that's a good thing :)

actually, just thinking about it, it'd be good if you could tell Lustre
(llite) to be lazy about re-stat'ing files in what is mostly an
un-changing read-only image. is it possible to do this?

>Certainly, I am not without bias, but the feature set of 1.8 looks
>compelling enough to make me want to upgrade my own little "dogfood"
>cluster here to 1.8.  :-)

yes, the features are shiny :)

cheers,
robin