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[netCDF #YTY-788071]: netcdf 4 GB variable size questions

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  • Subject: [netCDF #YTY-788071]: netcdf 4 GB variable size questions
  • Date: Mon, 21 May 2007 10:18:14 -0600
Jason,

With 3.6 it is possible to have multiple variables all with sizes larger than 4 
GiB, as long as they all use the record dimension, and each has no more than 4 
GiB per record.  When you create the file, you have to use a flag to the 
nc_create or nf90_create call to specify use of the 64-bit offset variant of 
the file format, as described in the documentation or in this FAQ:

http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#Large%20File%20Support8

So, for example, this is a possible structure for a netCDF file using version 
3.6

netcdf large_vars {
dimensions:
  k=unlimited;
  m=31700;
  n=31700;
  t=1;
variables:
  float var1(k,t,m,n);  // over 4 GB for each value of k
  float var2(k,t,m,n);  // over 4 GB for each value of k
  float var3(k,t,m,n);  // ...
}

If time will always be 1, there may be no need to use it as the unlimited 
dimension.  So if you could make one of your spatial dimensions the unlimited 
dimension, whichever is most slowly varying, then you could store multiple 
variables of very large size, as long as the space for each variable in each 
record didn't exceed the limit of 2**32-4 values.

--Russ

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



Ticket Details
===================
Ticket ID: YTY-788071
Department: Support netCDF
Priority: Normal
Status: Closed