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[netCDF #WCR-337446]: problems with NETCDF4

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  • Subject: [netCDF #WCR-337446]: problems with NETCDF4
  • Date: Wed, 15 Feb 2012 15:00:21 -0700
> Another (hopefully quick) question:
> How do I enable compression in NETCDF4?
> I opened the file with the following statement:
> iret = nf90_create(path=trim(fname),cmode=nf90_hdf5, ncid=ftn)
> 
> but I didn't notice any difference in the file sizes. I guess there are other 
> things I need to do?

Here's an answer to an FAQ on that:

   http://www.unidata.ucar.edu/netcdf/docs/faq.html#fv8

Compression is done on a variable-by-variable basis, so it's possible
to use different compression levels on different variables.  But if
you just want to compress all variables in the file using the same
compression level, the easiest way is using the nccopy utility, as in

  nccopy -d1 foo.nc foo-compressed.nc

to use "deflation level" 1.

Note that for small files, the compressed netCDF-4 files will
actually be larger than uncompressed netCDF-3 (classic format) files,
because the underlying HDF5 format has some fixed-size overhead.  But
for large datasets, compression will save space, at the expense of
taking more time to read and write the data.

I just tested the 4.1.3 nccopy on an example file for compression and got this:

 $ nccopy -d1 llnl.nc llnl-compressed.nc && ls -l llnl*.nc
 -rw-rw-r-- 1 russ ustaff 13802 Feb 15 14:58 llnl-compressed.nc
 -rw-rw-r-- 1 russ ustaff 32864 Oct 17 11:05 llnl.nc

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: WCR-337446
Department: Support netCDF
Priority: Normal
Status: Closed