The file create_hdf5.py contains an example of how to convert a tar file with images to an HDF5 file. Usage example:

python3 create_hdf5.py /path/to/image-data.tar

Converting a 26GB tar file with 1.3 million images took less than 10 minutes on Mahti.

The file pytorch_dvc_cnn_simple.py together with pytorch_dvc_cnn_simple.py shows a simple CNN image training that uses an HDF5 dataset. The original dataset can be found from https://a3s.fi/mldata/dogs-vs-cats.tar.

The main trick is that the HDF5 file needs to be opened in the __getitem__ method of the Dataset, as explained e.g. in this blog post by Soumya Tripathy