Study and test the HDF5 examples (hdf5.c or hdf5.f90) where the Simple MPI-IO exercise has been re-written with HDF5 using collective parallel write.
On Puhti, you will need to load the module hdf5/1.10.4-mpi before you can
compile the code:
module load hdf5/1.10.4-mpi
Compile and run the program. You can use the h5dump command to check the
values in a HDF5 file.