Re: Possibly of interest: parallel netcdf study

"Robert E. McGrath" <mcgrath@xxxxxxxxxxxxx> wrote:
> Possibly of interest:
> We have just posted a short study investigating parallel netCDF.
> Muqun Yang, Mike Folk, Robert E. McGrath, "Investigation of Parallel 
> NetCDF
>    with ROMS",
> This work was done as part of the NSF-funded MEAD project:

Thanks, this was interesting.  I think you want to change the table
heading in Table 1 from "NCAR IBM P690" to "NCSA IBM P690".  

I wonder if the results that show less wall clock time for 6 time
steps than for 4 time steps and similarly for 10 time steps less than
for 8 time steps with pnetCDF on the NCSA P690 might be an indication
of a discretization error in the timing.  Or maybe something else was
consuming enough of the machine that the results are unreliable.

I'm also curious why the pnetCDF appears to be so much slower than
serial netCDF for small writes.  Do you know what the nature of the
MPI-IO overhead is that could explain what appears to be a 10:1
slowdown for using pnetCDF with 4 time steps on the NCSA P690?  I
could understand maybe a 2:1 slowdown, but 10:1 seems surprisingly
large ...