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Re: simple question

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  • Subject: Re: simple question
  • Date: Mon, 02 May 2005 08:57:06 -0600
Hi Hannes,

> I create a nc file with dimensions x = 162 and y =  76
> with a daily timestep for 10 years, 4 variables ( 1 real, 3 integer)
> How large should such a file be....
> because just by creating it grows up to 568 MB.
> Is such size reasonable ? seems to be to large to me..

Each real or integer variable value takes 4 bytes.  So just the size
to store the values is about 162*76*360*10*4*4 or about 709 MB.

If you are using the unlimited dimension for time, then the file size
should only reflect the number of time steps you have actually
written.  So after writing one time step, the storage space for values
in the file should only be about 162*76*4*4 or about 200 KB.

For questions like this, it is helpful to send the structure of the
netCDF file, which you can get by running

  ncdump -h FILENAME

> Second question
> it is possible to open an netcdf file and write from several processes to it..
> I know already that several processes can have read access to one file, 
> with one process writing...

With netCDF-3, there should only be one writer.  If you need to have
multiple processes writing the same file concurrently, you can use
Parallel netCDF:

  http://www-unix.mcs.anl.gov/parallel-netcdf/

or wait until the release of netCDF 4, which will also support
parallel writing to a single file through MPI-IO in HDF5.

--Russ

_____________________________________________________________________

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