Chunked data are written in chunks of user-defined size.
A chunk is a hyper-rectangle of any shape. When a dataset is
chunked, each chunk is read or written as a single I/O operation,
and individually passed from stage to stage of the pipeline and
filters.
Chunked data is the default for netCDF-4 variables. (You may use
contiguous instead.)
Chunking is required for any variable that uses one or more
unlimited dimensions, compression or other filter.
Chunking is set when the variable is created, and is never changed
after that. To change the chunksize you have to copy the data into a
new file.
