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Subject: Re: [OMPI users] Problem with NFS + PVFS2 + OpenMPI
From: Robert Latham (robl_at_[hidden])
Date: 2008-05-29 15:41:56

On Thu, May 29, 2008 at 04:24:18PM -0300, Davi Vercillo C. Garcia wrote:
> Hi,
> I'm trying to run my program in my environment and some problems are
> happening. My environment is based on PVFS2 over NFS (PVFS is mounted
> over NFS partition), OpenMPI and Ubuntu. My program uses MPI-IO and
> BZ2 development libraries. When I tried to run, a message appears:
> File locking failed in ADIOI_Set_lock. If the file system is NFS, you
> need to use NFS version 3, ensure that the lockd daemon is running on
> all the machines, and mount the directory with the 'noac' option (no
> attribute caching).
> [] MPI_ABORT invoked on rank 0 in
> communicator MPI_COMM_WORLD with errorcode 1
> mpiexec noticed that job rank 1 with PID 5008 on node campogrande04
> exited on signal 15 (Terminated).


NFS has some pretty sloppy consistency semantics. If you want
parallel I/O to NFS you have to turn off some caches (the 'noac'
option in your error message) and work pretty hard to flush
client-side caches (which ROMIO does for you using fcntl locks). If
you do this, note that your performance will be really bad, but you'll
get correct results.

Your nfs-exported PVFS volumes will give you pretty decent serial i/o
performance since NFS caching only helps in that case.

I'd suggest, though, that you try using straight PVFS for your MPI-IO
application, as long as the parallell clients have access to all of
the pvfs servers (if tools like pvfs2-ping and pvfs2-ls work, then you
do). You'll get better performance for a variety of reasons and can
continue to keep your NFS-exported PVFS volumes up at the same time.

Oh, I see you want to use ordered i/o in your application. PVFS
doesn't support that mode. However, since you know how much data each
process wants to write, a combination of MPI_Scan (to compute each
processes offset) and MPI_File_write_at_all (to carry out the
collective i/o) will give you the same result with likely better
performance (and has the nice side effect of working with pvfs).


Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Lab, IL USA                 B29D F333 664A 4280 315B