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Re: mpi & netcdf

Hi Peter,

Back on June 2, I wrote a somewhat garbled answer to your question: 

> > I was naively trying to write an mpi program that
> > called netcdf where each processor wrote to the
> > same netcdf file. Each processor was trying to
> > write to the appropriate spot in the file. I was
> > trying to mimic what happens with a direct
> > access file in fortran. This is the usual way
> > I write things out with mpi and fortran. Can 
> > this be done ? My first attempts seemed to be
> > okay, but then i made time unlimited
> > and got junk out ?
> 
> The current implementation of netCDF is not designed to support
> multiple processors writing to the same file concurrently.  So the
> simple answer is it cannot be done using the current netCDF library.
> You can do parallel reads, but there can only be one writer.
> 
> We are beginning the development of a parallel version of netCDF based
> on HDF5 and its use of MPI-IO.  There are two other groups of
> researchers developing parallel netCDF I/O using MPI-IO directly
> (Northwestern/Argonne and NERSC).  No one has something ready to use
> yet, so unfortunately you'll have to serialize your netCDF output or
> use a different scientific data access interface, such as HDF5, until
> something is ready.  Our project with NCSA is funded by NASA and
> delivery of the reference implementation is currently planned to be
> available in Summer 2005.

There has been some significant progress in both the
Northwestern/Argonne effort:

   http://www-unix.mcs.anl.gov/parallel-netcdf/

and the NERSC version

   http://hpcf.nersc.gov/software/libs/io/netcdf/sp/pusage.html

It is possible to try out both of these now, with code that can be
downloaded from their respective sites.  The NERSC version  has a
Fortran interface.  If you try either of these out, we'd be interested
in the results.

--Russ

_____________________________________________________________________

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