PnetCDF, ROMIO & "noac" setting

[Carl Ponder]

*On 04/16/2018 11:25 PM, Wei-keng Liao wrote:*
>
>     Using NFS is discouraged for MPI-IO (and PnetCDF as well)
>     applications, because
>     it requires a special setting in NFS lock daemons to make it work
>     correctly for MPI-IO.
>     See ROMIO user guide at
>     ftp://ftp.mcs.anl.gov/pub/romio/users-guide/node12.html
>
>     If the HPC cluster you are using has a parallel file system, such
>     as Lustre or
>     OrangeFS, then you should use it.
>
Wei-keng -- my sysadmin's tell me that NFS is all that we're ever going 
to have on our cluster.
I can live with substandard I/O performance, I just want the various I/O 
libraries to give the right data.
We can try following these ROMIO instructions, but can you answer some 
questions about it?

1) It says that ROMIO is used in MPICH. Just to confirm, do MVAPICH2 & 
OpenMPI & Intel/MPI all use ROMIO?
     And even if not, would the instructions still be relevant to these 
other MPI's?

2) It talks about NFS version 3. It looks like we have a combination of 
3 & 4 on our system.
      Are the instructions relevant to NFS version 4?

3) Given the reservations about performance, I suppose I could ask for a 
special directory to be created & mounted for "coherent" operations, and 
leave the other mounts as-is.
     Do you see any problems with doing this?

Thanks,

                    Carl



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