<div dir="ltr">Thanks for your replies Dom and Wei-keng. <div><br></div><div>Yes, I gather that the pnetCDF library cannot produce NETCDF4 files, but I have also read that the NETCD4 library can do parallel input and output <a href="http://www.unidata.ucar.edu/software/netcdf/docs/parallel_io.html">http://www.unidata.ucar.edu/software/netcdf/docs/parallel_io.html</a>. So I guess what I was asking is: does anyone know how to get WRF to write in parallel to a NETCDF4 file? I am guessing that the answer is no, or someone would have mentioned it, but if it were possible I think that implementing it would be a very worthwhile project. </div><div><br></div><div>Yes, I can post-process the data to do the compression later, but the data volumes are very high (~1.2 TB per hour simulation time) so this sort of post-processing is a significant overhead. </div><div><br></div><div>Thanks for the suggestion of I/O quilting. I'll give it a try. </div><div><br></div><div>To answer you questions WEi-keng: I am using a lustre file system, and two versions of WRF: 3.7 compiled with pnetCDF, and 3.7.1 compiled with serial I/O. </div><div><br></div><div>Regards</div><div><br></div><div>Chris </div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Mar 5, 2016 at 11:16 PM, Wei-keng Liao <span dir="ltr"><<a href="mailto:wkliao@eecs.northwestern.edu" target="_blank">wkliao@eecs.northwestern.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi, Chris<br>
<br>
The file size difference may be due to data compression when WRF uses HDF5<br>
library internally to write NetCDF4 files. PnetCDF does not do compression.<br>
You can use "ncgen" to convert a netCDF classical file to netCDF conformed<br>
HDF5 files. See netCDF user guide for command-line options of ncgen.<br>
<a href="http://www.unidata.ucar.edu/software/netcdf/docs/netcdf_utilities_guide.html#guide_ncgen" rel="noreferrer" target="_blank">http://www.unidata.ucar.edu/software/netcdf/docs/netcdf_utilities_guide.html#guide_ncgen</a><br>
<br>
As for the files produced by PnetCDF, would you mind answering my<br>
2 questions. Were you writing the outputs to a Lustre file system,<br>
or the name of parallel file system you used if not Lustre?<br>
What version of WRF are you using?<br>
<span class="HOEnZb"><font color="#888888"><br>
Wei-keng<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
On Mar 4, 2016, at 3:54 AM, Christopher Thomas wrote:<br>
<br>
> Hi there,<br>
><br>
> Does anyone know how to compile WRF to use parallel NETCDF but still output NETCDF4 files?<br>
><br>
> I am using 512 cores and outputting data at high temporal and spatial resolutions; parallel NETCDF reduces my wall times by about 1/3 but more than doubles output file sizes over NETCDF4 serial output.<br>
><br>
> Chris<br>
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</div></div></blockquote></div><br></div>