[Lustre-discuss] Lustre clients under Xen

Andreas Dilger andreas.dilger at oracle.com
Tue Nov 30 13:27:18 PST 2010


On 2010-11-30, at 12:14, Lukas Hejtmanek wrote:
> I see some oddities on Lustre clients running under Xen DomU ...
> when the DomU is being suspended (most memory and CPU is stolen by another DomU).
> 
> Is this something known or unsupported? (I.e., running Lustre under Xen with domains preemption)

Lustre servers expect to always be able to communicate with the clients, and that the clients are responsive to their requests, or they are evicted by the server to keep the filesystem usable.  This makes sense in an HPC environment where the filesystem is a shared resource, and clients fail regularly (due to huge numbers of clients), and it is more important for the rest of the clients to continue.

There is a mode that the servers will NOT expect the clients to be responsive, but then it is the client's responsibility to act accordingly and check for pending server requests before it uses any saved state.  That is used by the "liblustre" code, but is not implemented for the normal Linux client.

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.  

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.




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