File System Issues

Most users do not need to worry about file systems. However, there are two issues: using NFS (the Network File System) with MPI-IO and using NFS with some automounters. These issues are covered in the next two sections.

NFS and MPI-IO

To use MPI-IO multihost on NFS file systems, NFS should be version 3, and the shared NFS directory must be mounted with the ``no attribute caching'' (noac) option set (the directory cannot be automounted). If NFS is not mounted in this manner, the following error could occur:

    MPI_Barrier: Internal MPI error: No such file or directory 
    File locking messages 

1. confirm you are running NFS version 3


    rpcinfo -p `hostname` | grep nfs 
 
    for example, there should be a '3' in the second column 
    fire >rpcinfo -p fire | grep nfs 
    100003    3   udp   2049  nfs 


2. edit /etc/fstab for each NFS directory read/written by MPI-IO on each machine used for multihost MPI-IO. The following is an example of a correct fstab entry for /epm1:


    root >grep epm1 /etc/fstab 
    gershwin:/epm1 /rmt/gershwin/epm1 nfs bg,intr,noac 0 0 

If the ``noac'' option is not present, add it and then remount this directory on each of the machines that will be used to share MPI-IO files.


    root >umount /rmt/gershwin/epm1 
    root >mount /rmt/gershwin/epm1 


3. confirm that the directory is mounted noac


    root >grep gershwin /etc/mnttab 
    gershwin:/epm1 /rmt/gershwin/epm1 nfs 
    noac,acregmin=0,acregmax=0,acdirmin=0,acdirmax=0 0 0 899911504