[Lustre-discuss] Lustre clients under Xen

[Oleg Drokin]

Hello!

On Dec 1, 2010, at 3:12 AM, Lukas Hejtmanek wrote:

> On Tue, Nov 30, 2010 at 02:27:18PM -0700, Andreas Dilger wrote:
>> Combining these two modes, for use in VM systems where the Linux client may
>> be unresponsive for long periods of time might makes sense, though it can
>> also add a lot of complexity.  I don't think anyone is planning to work on
>> this in the near future.  
> Thanks, however, the client is not completely unresponsive, it still has CPU
> and about 500MB RAM so it should be OK from Lustre point of view.
> Also, the problem arises as soon as I begin to shrink memory, e.g., from 8GB
> to 0.5GB. Sometimes, Lustre client hangs. Is there any conceptual problem with
> Lustre and memory shrinker in Xen?

It all depends on how Xen does the shrinking. If it blocks kernel code from execution for long periods of time in process,
it's the same as if the node is suspended for some time essentially.
Even if it would block only certain threads that tare trying to access to be shrunk memory and it happens to be certain lustre threads,
that would still spend trouble if the blocking persists for significant amounts of time.

I personally use XEN without memory shrinking for my testing and it seems to be working just fine.

Bye,
    Oleg