NFS and MPIO


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To use MPIO 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 

In order to reconfigure NFS to handle MPIO properly, the following sequence of steps are needed (root permission required):
    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 MPIO on each machine used for multihost MPIO. 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 MPIO 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 
    
    
Turning off of attribute caching may reduce performance of MPIO applications as well as other applications using this directory. The load on the machine where the nfs directory is hosted will increase.



Up: Contents Next: Thorough Testing Previous: Special Considerations for Running with Shared Memory