[Lustre-discuss] Performance parameters

[Brian J. Murrell]

On Wed, 2008-06-11 at 16:16 +0200, Enrico Morelli wrote:
> 
> Because we thought that Lustre was better than NFS

For certain workloads, yes, it is much better because...

>  and more scalable

It is very much more scalable, but with such tremendous scalability
there is a cost at the very low end (and a single server for MDT and
OSTS is about as low as you can get on the scale) of the scale.

> also in a simple configuration like our.

For a single server serving both MDT and OSTs on a general file sharing
workload, Lustre will not typically perform any better than NFS.  There
are exceptions to this generalization for certain corner cases, but in
general it's pretty accurate.

> Now, if I reduce the OSTs to one do you think that I can improve the
> performance?

Not really.  You are still running into the same basic problem in that
you are trying to serve up to completely different data sets (meta-data
and file data) from the same device.

If you could isolate your MDT to it's own device (i.e. a couple of small
sata disks mirrored on their own sata buses is pretty cheap) you might
see some improvement, but you might also run into other bottlenecks that
a single server will impose, such as bus bandwidth, memory bandwidth,
network bandwidth, etc.

b.

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