• 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.
• Chunking is transparent to the reader.

2008 Unidata NetCDF Workshop for Developers and Data Providers > Chunking Data with NetCDF-4