[Lustre-discuss] OSS on compute nodes

[Chris Worley]

On Fri, Apr 11, 2008 at 10:34 AM, Brian J. Murrell
<Brian.Murrell at sun.com> wrote:
> On Fri, 2008-04-11 at 20:29 +0400, Peter Avakian wrote:
>  >
>  > Do you see any problem in having each compute node, within a grid,
>  > acting as an OSS server via the separate IB channel on the fabric? My
>  > compute nodes have built-in raid controllers.
>
>  If by compute nodes you mean Lustre clients, then yes, this is a problem
>  and an unsupported configuration.  The reason is because memory
>  pressures on a client/OSS machine can cause a deadlock.

What if either the compute node or (most likely) the OSS was in a VM
(and make sure to not overcommit processors)?

Chris
>
>  The client tries to flush pages to an OST to relieve memory pressure.
>  An OST needs to allocate memory in order to process page flushes from a
>  client.  If a client trying to relieve memory pressure tries to flush
>  pages to an OST on the same node, the OST will get failures trying to
>  allocate memory (which is already under pressure) to fulfill the request
>  from the client.  Deadlock.
>
>  b.
>
>
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