Changing default for HierarchyFileOutputFormat to 1 (ASCII) instead of 2 (ASCII + HDF5). The HDF5 format does not scale well and can take ~10-50x longer than the actual datadump for simulations with >100k grids. We can set this back to the HDF5 format once the scaling issues are resolved.
@jwise77 do you think it would be more performant if it avoided attributes?
I'm not sure whether the hotspot lies in writing the attributes, creating the groups, or creating the links. I have done any timings in the routines, but I think it would be worthwhile to investigate.