netCDF  4.2.1.1
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The Default Chunking Scheme in version 4.1

(and 4.1.1)

When the data writer does not specify chunk sizes for variable, the netCDF library has to come up with some default values.

The C code below determines the default chunks sizes.

For unlimited dimensions, a chunk size of one is always used. Users are advised to set chunk sizes for large data sets with one or more unlimited dimensions, since a chunk size of one is quite inefficient.

For fixed dimensions, the algorithm below finds a size for the chunk sizes in each dimension which results in chunks of DEFAULT_CHUNK_SIZE (which can be modified in the netCDF configure script).

/* Unlimited dim always gets chunksize of 1. */
if (dim->unlimited)
chunksize[d] = 1;
else
chunksize[d] = pow((double)DEFAULT_CHUNK_SIZE/type_size,
1/(double)(var->ndims - unlimdim));

Generated on Wed Aug 22 2012 14:39:40 for netCDF. NetCDF is a Unidata library.