Dear Petsc Team! I had an issue when writing out DMPlex objects through hdf5. This comes from a DMLabel that has only entries on non-local mesh points. The DMLabel write only includes local parts of the label and so leads to a zero sized write for the index set. This seems to be fine except that the hdf5 chunksize is set to zero which is not allowed. I added a minimal example to illustrate the error. It creates a 2D DMPlex in serial, distributes it, labels the nonlocal points in the mesh and dumps it via PetscObjectViewer to HDF5. Run with: make plex.h5 I also attached a quick fix to override the chunksize. Please let me know if you anything extra and also if this is expected behavior... I could certainly with the fact that DMLabel is not supposed to work this way. Many thanks, Fabian