@stanwest Can you suggest how to fix this merge conflict please?

Sure. I recommend the following before the return statement in xarray.core.dataset._get_chunk:

```python

Warn where requested chunks break preferred chunks, provided that the variable

contains data.

if var.size: for dim, size, chunk_sizes in zip(dims, shape, chunk_shape): try: preferred_chunk_sizes = preferred_chunks[dim] except KeyError: continue # Determine the stop indices of the preferred chunks, but omit the last stop # (equal to the dim size). In particular, assume that when a sequence # expresses the preferred chunks, the sequence sums to the size. preferred_stops = ( range(preferred_chunk_sizes, size, preferred_chunk_sizes) if isinstance(preferred_chunk_sizes, Number) else itertools.accumulate(preferred_chunk_sizes[:-1]) ) # Gather any stop indices of the specified chunks that are not a stop index # of a preferred chunk. Again, omit the last stop, assuming that it equals # the dim size. breaks = set(itertools.accumulate(chunk_sizes[:-1])).difference( preferred_stops ) if breaks: warnings.warn( "The specified Dask chunks separate the stored chunks along " f'dimension "{dim}" starting at index {min(breaks)}. This could ' "degrade performance. Instead, consider rechunking after loading." ) ```