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Subject: Re: [OMPI users] MPI_File_write hangs on NFS-mounted filesystem
From: Dmitry N. Mikushin (maemarcus_at_[hidden])
Date: 2013-11-07 12:21:08


Not sure if this is related, but:

I've seen a case of performance degradation on NFS and Lustre when
writing NetCDF files. The reason was that the file was filled with a
loop writing one 4-byte record at once. Performance became close to
local hard drive, when I simply introduced buffering of records and
writing them to files with one row at once.

- D.

2013/11/7 Steven G Johnson <stevenj_at_[hidden]>:
> The simple C program attached below hangs on MPI_File_write when I am using an NFS-mounted filesystem. Is MPI-IO supported in OpenMPI for NFS filesystems?
>
> I'm using OpenMPI 1.4.5 on Debian stable (wheezy), 64-bit Opteron CPU, Linux 3.2.51. I was surprised by this because the problems only started occurring recently when I upgraded my Debian system to wheezy; with OpenMPI in the previous Debian release, output to NFS-mounted filesystems worked fine.
>
> Is there any easy way to get this working? Any tips are appreciated.
>
> Regards,
> Steven G. Johnson
>
> -----------------------------------------------------------------------------------
> #include <stdio.h>
> #include <string.h>
> #include <mpi.h>
>
> void perr(const char *label, int err)
> {
> char s[MPI_MAX_ERROR_STRING];
> int len;
> MPI_Error_string(err, s, &len);
> printf("%s: %d = %s\n", label, err, s);
> }
>
> int main(int argc, char **argv)
> {
> MPI_Init(&argc, &argv);
>
> MPI_File fh;
> int err;
> err = MPI_File_open(MPI_COMM_WORLD, "tstmpiio.dat", MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &fh);
> perr("open", err);
>
> const char s[] = "Hello world!\n";
> MPI_Status status;
> err = MPI_File_write(fh, (void*) s, strlen(s), MPI_CHAR, &status);
> perr("write", err);
>
> err = MPI_File_close(&fh);
> perr("close", err);
>
> MPI_Finalize();
> return 0;
> }
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