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Hi Rob, On Sep 14, 2007, at 6:16 PM, Robert Latham wrote:
Hi. Bet you're going to get tired of me soon!
No, I'm happy to help you out, keep 'em coming... :-)
I'd really like to see all I/O calls using MPI-IO instead of posix fread (as in nc_check_for_hdf5). The HDF5 guys might recognize that I've bugged them about this last year :> ROMIO can take a file system prefix to override automatic file system detection. Such a prefix could be "testfs:" for our tracing file system driver (does no I/O, but logs which processes wrote how much) or it could be "pvfs2:" if we want to acess this userspace file system and do not happen to have the kernel component running. So for example, in nc_check_for_hdf5, instead of using fread, maybe use MPI_File_open and MPI_File_read when examining the magic number, and USE_PARALLEL_MPIIO is defined. Likewise, nc4_create_file, and nc_get_file_version use POSIX calls.
I think you might want the "MPI-POSIX" driver in HDF5 (look at H5Pset_fapl_mpiposix), but I don't know if the netCDF-4 library is exporting a way to use that in netCDF-4 applications. Hmm, but re- reading your note again, I'm not certain. Can you take a look at the MPI-POSIX file driver and see if that's what you want?
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