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Hi I'm continuing to look at NetCDF-4 and have found that it's not actually doing collective I/O. Even though it's the default, I've called nc_var_par_access with NC_COLLECTIVE just to be sure. I can verify in Jumpshot that all (in this case) 4 processors are calling independent I/O routines (MPI_File_write_at), even though I was expecting to see collective I/O (MPI_File_write_all or MPI_File_write_at_all). This appears to be the case for both writes and reads. In case it matters, I'm using an exceedingly small dataset. ==rob -- Rob Latham Mathematics and Computer Science Division A215 0178 EA2D B059 8CDF Argonne National Lab, IL USA B29D F333 664A 4280 315B
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