Datasets with early allocation and unlimited dimensions (Extensible Array, version-2 B-tree, version-1 B-tree under earliest), unfiltered and deflated: the random resize workload gives the values h5py gets and the same chunk index shape, with every chunk a growth brings in allocated and filled as H5D__chunk_allocate does. Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>