Scot Breitenfeld from The HDF Group describes on the group blog parallel file extensions to CGNS. The CFD General Notation System (CGNS) provides a general, portable, and extensible standard for the storage and retrieval of computational fluid dynamics (CFD) analysis data. It consists of a collection of conventions, and free and open software implementing those conventions. It is self-descriptive, machine-independent, well-documented, and administered by an international steering committee. It is also an American Institute of Aeronautics and Astronautics (AIAA) Recommended Practice.
CGNS data was originally stored using a file format called ADF ('Advanced Data Format'), but ADF does not have parallel I/O or data compression capabilities, and does not have the support base and tools that HDF5 offers. ADF has since been superseded by the Hierarchical Data Format, Version 5 (HDF5) as the official default underlying storage mechanism for CGNS.
In 2014, NASA provided funding for The HDF Group to improve the under-performing parallel capabilities of the CGNS library.