[Lustre-discuss] Lustre client and OST on same machine

[Andreas Dilger]

On 2012-02-15, at 3:58 AM, Jack David wrote:
> On Wed, Feb 15, 2012 at 5:00 PM, Peter Grandi <pg_lus at lus.for.sabi.co.uk> wrote:
>>> Once the lustre client knows about the stripe information of a
>>> file, will it directly communicate to OSS?
>>> 
>>> If yes, is there any optimization possible if lustre client
>>> learns that the data is in the same machine (when acting as
>>> OST) ?
>> 
>> Not directly. RPCs may be rather faster locally than over a
>> network interface.
> 
> Hmm, but it will still involve multiple memory copy operations to
> transfer data from _local_ client to _local_ OST, correct? Can that be
> avoided? or The client is smart enough to share the memory when it
> knows the client and OST are the same machine.

There is still a memory copy, but it is internal to the LNET code
for the lo at 0 interface and is not being passed over e.g. the TCP
loopback or ethernet lo interface.

It would be desirable to have a more efficient OSC->OSD interface for
local IO, but as yet there hasn't been any work in this direction.

Cheers, Andreas
--
Andreas Dilger                       Whamcloud, Inc.
Principal Lustre Engineer            http://www.whamcloud.com/