issue_comments: 625857192

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https://github.com/pydata/xarray/issues/4046#issuecomment-625857192 https://api.github.com/repos/pydata/xarray/issues/4046 625857192 MDEyOklzc3VlQ29tbWVudDYyNTg1NzE5Mg== 1197350 2020-05-08T14:59:43Z 2020-05-08T14:59:43Z MEMBER

Thanks for raising this useful issue.

There are two ways to control Zarr chunks: - Specify chunks in encoding (always takes precedence) - Determine chunks based on Dask chunks

If neither of these are present, Xarray creates the zarr arrays with no chunks specified. In this case, zarr will choose the chunks automatically for you. This behavior is described in the Zarr docs: https://zarr.readthedocs.io/en/stable/tutorial.html#chunk-size-and-shape

If you are feeling lazy, you can let Zarr guess a chunk shape for your data by providing chunks=True, although please note that the algorithm for guessing a chunk shape is based on simple heuristics and may be far from optimal

You can override this default per variable by specifying a single global chunk in encoding: python ds.foo.encoding['chunks'] = -1 or, at write time, python ds.to_zarr('test.zarr', mode='w', encoding={'foo': {'chunks': -1}})

I agree that none of this is described well in the Xarray docs. A PR to improve the docs would be most welcome. 😉 

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