[netcdf-hdf] collective I/O ?


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

This appears to be the case for both writes and reads. 

In case it matters, I'm using an exceedingly small dataset. 


Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Lab, IL USA                 B29D F333 664A 4280 315B