By default, the header has almost no extra space; it is just large enough to contain the dimensions, attributes (including all attribute values), and variable metadata, rounded up to a whole number of disk blocks.

• Advantage: netCDF files are compact, with little overhead
• Disadvantage: schema changes may require moving all the data:
  • defining new dimensions, variables, or attributes in an existing file
  • renaming existing dimensions, variables, or attributes with longer names
  • redefining an attribute to have values of a larger type or more values, such as a longer string value

To avoid copying data when the file schema changes, either

• create all necessary dimensions, variables, and attributes before writing data, or
• reserve extra space in the file header for later additions (using nc__enddef() in C, NF__ENDDEF() or NF90__ENDDEF() for Fortran, setExtraHeaderBytes() method of NetcdfFileWritable for Java)

2009 Unidata NetCDF Workshop for Developers and Data Providers > Formats and Performance