Document ROMIO/HDF5/Chunking issue

open-mpi/ompi#7795

docs/source/backends/hdf5.rst

@@ -100,6 +100,12 @@ Known Issues
    Collective HDF5 metadata reads (``OPENPMD_HDF5_COLLECTIVE_METADATA=ON``) broke in 1.10.5, falling back to individual metadata operations.
    HDF5 releases 1.10.4 and earlier are not affected; versions 1.10.9+, 1.12.2+ and 1.13.1+ fixed the issue.
 
+.. warning::
+
+   The ROMIO backend of OpenMPI has `a bug <https://github.com/open-mpi/ompi/issues/7795>`_ that leads to segmentation faults in combination with parallel HDF5 I/O with chunking enabled.
+   This bug usually does not occur when using default configurations as OpenMPI `uses the OMPIO component by default <https://docs.open-mpi.org/en/v5.0.x/mca.html>`_.
+   The bug affects at least the entire OpenMPI 4.* release range and is currently set to be fixed for release 5.0 (release candidate available at the time of writing this).
+
 
 Selected References
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