Specify chunks in bytes

Is your feature request related to a problem?

I'm playing around with xarray performance and would like a way to easily tweak chunk sizes. I'm able to do this by backing out what xarray chooses in an open_zarr call and then provide the right chunks= argument. I'll admit though that I wouldn't mind giving Xarray a value like "1 GiB" though and having it use that when determining "auto" chunk sizes.

Dask array does this in two ways. We can provide a value in chunks as like the following:

x = da.random.random(..., chunks="1 GiB")

We also refer to a value in Dask config

In [1]: import dask

In [2]: dask.config.get("array.chunk-size")
Out[2]: '128MiB'

This is not very important (I'm unblocked) but I thought I'd mention it in case someone is looking for some fun work 🙂

Describe the solution you'd like

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Describe alternatives you've considered

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Additional context

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Start by tracing xarray's open_zarr chunks= handling and the auto chunk-size path, then compare the requested byte-size syntax with Dask array chunks and the dask.config array.chunk-size setting. Done means users can provide a value such as "1 GiB" when determining automatic chunk sizes, with coverage for the supported behavior.