[netCDF #UUS-259413]: pnetcdf and netcdf

Hi John,

> Is it possible to write a large variable (>4GB) to a file with pnetcdf and 
> read back the variable from the resulting file with netcdf? Outputting a 
> large variable with pnetcdf appears to require passing the NC_64BIT_DATA flag 
> (not NC_64BIT_OFFSET) to nc_create_par() - without this flag an error is 
> generated. The file is written successfully, but when NC_64BIT_DATA is used 
> the file is unrecognized by netcdf. For example:
> 
> yslogin2[43] ncdump -h vx.0000.nc0
> ncdump: vx.0000.nc0: NetCDF: Unknown file format
> 
> From what I can gather from the web the NC_64BIT_DATA results in the 
> generation of a CDF-5 formatted file. Is there support for CDF-5 in netCDF, 
> or any other options for mixing pnetcdf and netCDF?

Are you using just pnetcdf, or the netCDF-4/pnetcdf integration described here:

  http://trac.mcs.anl.gov/projects/parallel-netcdf/wiki/PnetcdfAndNetcdf4

and in the last two bullets here:

  
http://www.unidata.ucar.edu/software/netcdf/workshops/2010/pnetcdf/PnetCDF.html

when built as described with the --enable-pnetcdf flag in the last paragraph 
here:

  http://www.unidata.ucar.edu/software/netcdf/docs/build_parallel.html

Ed Hartnett did that integration before he left, and we don't know much more 
about
it, but I'm just integrating some pnetcdf fixes from Greg Sjaardema at Sandia 
into
our trunk for a netcdf-4.3 release, so I'm trying to get the pnetcdf tests 
working.

On the subject of CDF-5, Rob Latham contributed the code needed to integrate 
support 
for CDF-5 into netCDF-4, as described in this Jira ticket, but the work hasn't 
been
done yet:

  https://www.unidata.ucar.edu/jira/browse/NCF-163

It would require that we also change netCDF-Java to read (and eventually write) 
the
new forat as well.  I've discussed that with John Caron, and he thought it 
wouldn't
require too much work, so we should eventually do it.  We're a little short of 
resources
now, with only two of us working on netCDF C and Fortran, but I suspect it 
won't get
any easier to integrate Rob Latham's changes into netCDF as we continue to 
refactor it,
though recent work on the dispatch layer might actually make it easier.

If it would be of any use to you, I could pass on the CDF-5 patches ...

--Russ

> thanks!
> 
> John Clyne
> National Center for Atmospheric Research
> 303.497.1236 (w), 303.809.1922 (c)
> address@hidden
> 
> 
> 
Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: UUS-259413
Department: Support netCDF
Priority: Normal
Status: Closed