Hi All,
I implemented the parallel I/O in ROMS (http://www.myroms.org) using
the latest snapshot of the NetCDF-4/HDF5 libraries.
I have two questions:
(1) The documentation for "nf90_open_par" says that it is only
possible to open a NetCDF4 format file for parallel processing.
This makes sense if the file is open for writing. However,
I think that it should be able to open a classic format file
(NetCDF 3.x) for just reading since the library is backward
compatible. I tested this in ROMS and in fact it is reading
a classic format in parallel as far as I can see in the
debugger. I am not going inside the libraries. So the
question is this actually happening? Is the library reading
a classic format in parallel? If so, perhaps the documentation
needs to be revised.
http://www.unidata.ucar.edu/software/netcdf/docs_snapshot/netcdf-f90.html#NF90_005fOPEN_005fPAR
(2) Why doesn't the library create identical files with the
same executable? Are there any time makings or other execution
information hidden in the created NetCDF-4 file. I tried to run
the same execute twice and a binary difference tells me
that the files are different:
> diff new.nc old.nc
Binary files new.nc and old.nc differ
However, if I dump the data into ASCII files, using "ncdump", the
files are identical.
I need to understand this issue because this is an important
parallel partition test. Regardless of the parallel partition
or number of MPI nodes, we should get identical solutions.
Otherwise, we have a parallel bug.
If there is an internal marking, how should we deactivate it?
Thank you, H
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Hernan G. Arango Institute of Marine and Coastal Sciences
arango@xxxxxxxxxxxxxxxxxx Rutgers University
off: (732) 932-6555 x266 71 Dudley Road
FAX: (732) 932-6520 New Brunswick, NJ 08901-8521, USA
http://marine.rutgers.edu/po/arango
http://marine.rutgers.edu/po/arango/rocco
http://marine.rutgers.edu/roms
http://www.myroms.org
http://www.ocean-modeling.org
