On Sep 17, 2005, at 11:22 AM, Dave Hagedorn wrote:
> Just wondering if anyone has noticed any performance differences in
> runnnig lam off of an NFS mount as opposed to running locally.
>
> We've got a 14-node cluster set up where I work. There is also a
> storage server with a RAID array. All of the nodes and storage server
> are connected with gigabit ethernet through a single switch. We've
> stored lam + our program (LS-DYNA) on an NFS mount which all of the
> nodes access. In addition, our home directories are mounted via NFS,
> so all output fies from LS-DYNA gets sent across the netowrk. These
> files typically amount to 2 GB or so, usually written over the course
> of a days or more.
>
> Does anyone think this setup could cmpromise overall performance? We
> haven't tried intstalling anything locally - the NFS setup is really
> convenient.
There's always going to be some performance hit when all your disk I/
O and MPI communication go over the same network. I'd be more
concerned with home directories (and therefore your LS_DYNA data)
over NFS than I would be about some "site-local" packages that live
in NFS on the cluster. Your startup times for LAM might be a bit
lower using NFS instead of local disk, but on a 14 node cluster, it
should be more than manageable. And once the programs are up and
running, they should mostly be mapped into memory and not be a
problem. If you are running really close to your physical memory,
you might see extra NFS traffic as parts of LAM and your application
get flushed out to disk, but that's about it.
I'm not sure how big LS-DYNA's input and output data files are, but
they are surely bigger than LAM's binaries. So I'd be inclined to
worry more about them than anything else.
Brian
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