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Re: netCDF and NFS

Hi Nancy,

> Is there a problem writing netCDF files to a NFS cross-mounted disk?  

No, we do this all the time, and it works fine.  A few people have reported
problems with NFS writes, but they all turned out to be problems with the
NFS configuration or neglecting to call ncclose (or NCCLOS for Fortran) to
close a netCDF file before exiting.

> The problem seems to be with the temp files created as the netCDF 
> file is written.  If the output disk is crossmounted, the 
> temp files contain zeros, and the final output netCDF file
> contains a lot of zeros too.  Here is what we see:
> 
> o The problem occurs whether or not the input file is local, but only if 
>   the output file is remote.
> o The output data, when it is bad (all zeroes), is bad as it leaves
>   corona (the Unix cpu where the file is being written).

If corona is an HPUX platform, you might check that the netCDF library was
built with the patch described in the "Known Problems with NetCDF" document
at

    http://www.unidata.ucar.edu/packages/netcdf/known_problems.html

because if not, the symptoms might be similar to what you are seeing.

> o The problem does not occur when input and output files are local to 
>   corona.
> o The problem occurs regardless of whether the remote output file system 
>   is VMS  or Unix.  I copied the input file to a cross-mounted 
>   Unix disk and ran the program on that data, and the output file was full 
>   of the problem zeroes pretty consistently.
> 
> Is this a known problem, and we simply can't write netCDF files on 
> remote NFS cross-mounted disks?  Thanks very much, Nancy Soreide

If the problem is not due to the HPUX bug or neglecting to call ncclose() (or
ncsync() to flush the buffers if you are looking at the file while it is
still open), then we would be interested in a small program that
demonstrates the problem, so we could try to reproduce it here.

--Russ

______________________________________________________________________________

Russ Rew                                           UCAR Unidata Program
address@hidden                              http://www.unidata.ucar.edu