[Lustre-discuss] MGS - one per site

[David Dillow]

On Fri, 2009-06-26 at 22:05 +0200, Andreas Dilger wrote:
> On Jun 26, 2009  10:52 -0500, Carlos Santana wrote:
> > Can a lustre file system have more than one MGS? Isn't it only one per
> > site? I saw some examples where target type mgs was mentioned during
> > mkfs.lustre for MDS and OSS nodes. Is it correct and when is it used?
> 
> It makes sense generally to have a single MGS per site for multiple
> filesystems, because if clients are mounting more than one filesystem
> they can only communicate with a single MGS at a time.
> 
> In some cases there will of course be a need for multiple MGSes in
> a single site (e.g. secure and open networks), which is fine as long
> as clients don't try to mount from multiple MGSes at once.

What kind of problems could this cause?

We've had this configuration on both segments of Jaguar for some time
now with no ill effects that we could attribute to mounting from two
MGSes at the same time -- well, maybe that is not entirely true, as one
is an MGS, and the other is a combined MGS/MDS. Some clients are talking
with up to five separate combined MGS/MDS.
-- 
Dave Dillow
National Center for Computational Science
Oak Ridge National Laboratory
(865) 241-6602 office