[netcdf-hdf] collective I/O ?

• To: netcdf-hdf@xxxxxxxxxxxxxxxx
• Subject: [netcdf-hdf] collective I/O ?
• From: robl@xxxxxxxxxxx (Robert Latham)
• Date: Mon, 17 Sep 2007 17:06:52 -0500

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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