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Hierarchical Data Format version 5 (HDF5) is a set of file formats, libraries, and tools for storing and managing large scientific datasets. Originally developed at the National Center for Supercomputing Applications, it is currently supported by the non-profit HDF Group.

HDF5 is different product from previous versions of software named HDF, representing a complete redesign of the format and library. It also includes improved support for parallel I/O. The HDF5 file format is not compatible with HDF 4.x versions.


h5toh4 and h4toh5 converters are available on all NERSC machines.

Using HDF5 at NERSC

Cray provides native HDF5 libraries for each of the three PrgEnvs. The module cray-hdf5 provides a serial HDF5 I/O library:

module load cray-hdf5
ftn my_serial_hdf5_code.f90

while cray-hdf5-parallel provides a parallel HDF5 implementation:

module load cray-hdf5-parallel
ftn my_parallel_hdf5_code.f90

After loading one of those modules, one can continue to use the Cray compiler wrappers cc, CC, and ftn to compile HDF5 applications without requiring any additional flags to the compiler:

Other HDF5 tools at NERSC

NERSC provides several additional tools which allow users to interact with HDF5 data.


The H5py package is a Pythonic interface to the HDF5 library.

H5py provides an easy-to-use high level interface, which allows an application to store huge amounts of numerical data, and easily manipulate that data from NumPy. H5py uses straightforward Python and NumPy metaphors, like dictionaries and NumPy arrays. For example, you can iterate over datasets in a file, or check the .shape or .dtype attributes of datasets. You don't need to know anything special about HDF5 to get started. H5py rests on an object-oriented Cython wrapping of the HDF5 C API. Almost anything you can do in HDF5 from C, you can do with h5py from Python.

H5py at NERSC

If you want to use H5py with MPI-IO, then parallel H5py is recommended, which is available via:

module load python
module load h5py-parallel

If you use H5py for serial I/O, you can load NERSC's Anaconda Python module python.

numpy.dtype has the wrong size, try recompiling

This warning happens when the loaded python module is not what H5py is built with. You should load the python module for serial H5py, or h5py-parallel (after loading python) for parallel H5py.


HDF5 Utility Toolkit (H5hut) is a veneer API for HDF5: H5hut files are also valid HDF5 files and are compatible with other HDF5-based interfaces and tools. For example, the h5dump tool that comes standard with HDF5 can export H5hut files to ASCII or XML for additional portability. H5hut also includes tools to convert H5hut data to the Visualization ToolKit (VTK) format and to generate scripts for the Gnuplot data plotting tool.

Using H5hut at NERSC

For serial HDF5 code:

module load cray-hdf5
module load h5hut
cc my_serial_h5hut_code.c

For parallel HDF5 code:

module load cray-hdf5-parallel
module load h5hut-parallel
cc my_parallel_h5hut_code.c

Further information about HDF5