zarr-fill-value · shipping

Zarr fill value

A Zarr fill value is the array-metadata value used to represent uninitialized elements, including absent chunk data under the format's read semantics.

Related Observatory article: Zarr fill value on hesela.com

Interpretation: a storage fill value is not automatically a scientific missing-value mask. Consumer decoding can treat that value as ordinary data or map it to a missing marker. [1] [4]

Elision: omitting a chunk whose contents are entirely fill can be an intentional storage optimization. A never-written chunk and a previously written then deleted chunk can leave the same final store, so absence needs an external completeness expectation. [5]

Strict reads: Zarr-Python 3.4.1 with effective read_missing_chunks=False rejected missing selected store objects in Hesela's tests, but accepted empty inner chunks in a present shard. Verify effective runtime configuration and intended sparsity separately. [3] [2] [5]

Consumer scope: the measured Xarray reduction results cover 2025.10.1 and 2026.9.0 over Zarr 3.1.3, not all readers or current versions. [5]

Relations

related

Zarr, Zarr consolidated metadata, HDF5 fill value

Citations

1. Zarr format 3 core specification: fill values and array reads (accessed 2026-10-23)
2. Zarr sharding codec 1.0: empty inner chunks and index layout (accessed 2026-10-23)
3. Zarr-Python: runtime array configuration (accessed 2026-10-23)
4. Xarray 2025.10.1: open_zarr decoding contract (accessed 2026-10-23)
5. Hesela: Zarr archive acceptance observations (accessed 2026-10-23)

JSON: /data/terms/zarr-fill-value.json