This might be just a documentation issue, so sorry if this is not a problem with xarray.

I'm trying to save an intermediate result of a calculation with xarray + dask to disk, but I'd like to preserve the on-disk chunking. Setting the encoding of a Dataset.data_var or DataArray using the encoding attribute seems to work for (at least) some encoding variables, but not for chunksizes. For example:

``` python import xarray as xr import dask.array as da from dask.distributed import Client from IPython import embed

First generate a file with random numbers

rng = da.random.RandomState() shape = (10, 10000) chunks = [10, 10] dims = ['x', 'y'] z = rng.standard_normal(shape, chunks=chunks) da = xr.DataArray(z, dims=dims, name='z')

Set encoding of the DataArray

da.encoding['chunksizes'] = chunks # Not conserved da.encoding['zlib'] = True # Conserved ds = da.to_dataset() print(ds['z'].encoding) #out: {'chunksizes': [10, 10], 'zlib': True}

This one is chunked and compressed correctly

ds.to_netcdf('test1.nc', encoding={'z': {'chunksizes': chunks}})

While this one is only compressed

ds.to_netcdf('test2.nc') ```

Before this fix chunksizes was dropped even when original_shape was not found in encoding

• [x] Closes #2198
• [x] Tests added (for all bug fixes or enhancements)
• [x] Tests passed (for all non-documentation changes)

Four seemingly unrelated tests failed ``` python _____________ TestEncodeCFVariable.test_missing_fillvalue ________________

self = <xarray.tests.test_conventions.TestEncodeCFVariable testMethod=test_missing_fillvalue>

def test_missing_fillvalue(self):
    v = Variable(['x'], np.array([np.nan, 1, 2, 3]))
    v.encoding = {'dtype': 'int16'}
    with pytest.warns(Warning, match='floating point data as an integer'):

      conventions.encode_cf_variable(v)

E Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) was emitted. The list of emitted warnings is: [SerializationWarning('saving variable None with floating point data as an integer dtype without any _FillValue to use for NaNs',)].

xarray/tests/test_conventions.py:89: Failed ----------------------------------------------------------------------------------------------- Captured stderr call ----------------------------------------------------------------------------------------------- /usr/lib/python3.6/site-packages/pytest/vendored_packages/pluggy.py:248: SerializationWarning: saving variable None with floating point data as an integer dtype without any _FillValue to use for NaNs call_outcome = _CallOutcome(func) _____________ TestAccessor.test_register ______________

self = <xarray.tests.test_extensions.TestAccessor testMethod=test_register>

def test_register(self):

    @xr.register_dataset_accessor('demo')
    @xr.register_dataarray_accessor('demo')
    class DemoAccessor(object):
        """Demo accessor."""

        def __init__(self, xarray_obj):
            self._obj = xarray_obj

        @property
        def foo(self):
            return 'bar'

    ds = xr.Dataset()
    assert ds.demo.foo == 'bar'

    da = xr.DataArray(0)
    assert da.demo.foo == 'bar'

    # accessor is cached
    assert ds.demo is ds.demo

    # check descriptor
    assert ds.demo.__doc__ == "Demo accessor."
    assert xr.Dataset.demo.__doc__ == "Demo accessor."
    assert isinstance(ds.demo, DemoAccessor)
    assert xr.Dataset.demo is DemoAccessor

    # ensure we can remove it
    del xr.Dataset.demo
    assert not hasattr(xr.Dataset, 'demo')

    with pytest.warns(Warning, match='overriding a preexisting attribute'):
        @xr.register_dataarray_accessor('demo')

      class Foo(object):

E Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) was emitted. The list of emitted warnings is: [AccessorRegistrationWarning("registration of accessor <class 'xarray.tests.test_extensions.TestAccessor.test_register.\<locals>.Foo'> under name 'demo' for type <class 'xarray.core.dataarray.DataArray'> is overriding a preexisting attribute with the same name.",)].

xarray/tests/test_extensions.py:60: Failed ----------------------------------------------------------------------------------------------- Captured stderr call ----------------------------------------------------------------------------------------------- /home/karel/working/xarray/xarray/tests/test_extensions.py:60: AccessorRegistrationWarning: registration of accessor <class 'xarray.tests.test_extensions.TestAccessor.test_register.\<locals>.Foo'> under name 'demo' for type <class 'xarray.core.dataarray.DataArray'> is overriding a preexisting attribute with the same name. class Foo(object): ______________ TestAlias.test ______________

self = <xarray.tests.test_utils.TestAlias testMethod=test>

def test(self):
    def new_method():
        pass
    old_method = utils.alias(new_method, 'old_method')
    assert 'deprecated' in old_method.__doc__
    with pytest.warns(Warning, match='deprecated'):

      old_method()

E Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) was emitted. The list of emitted warnings is: [FutureWarning('old_method has been deprecated. Use new_method instead.',)].

xarray/tests/test_utils.py:28: Failed ----------------------------------------------------------------------------------------------- Captured stderr call ----------------------------------------------------------------------------------------------- /home/karel/working/xarray/xarray/tests/test_utils.py:28: FutureWarning: old_method has been deprecated. Use new_method instead. old_method() _____________ TestIndexVariable.test_coordinate_alias ______________

self = <xarray.tests.test_variable.TestIndexVariable testMethod=test_coordinate_alias>

def test_coordinate_alias(self):
    with pytest.warns(Warning, match='deprecated'):

      x = Coordinate('x', [1, 2, 3])

E Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) was emitted. The list of emitted warnings is: [FutureWarning('Coordinate has been deprecated. Use IndexVariable instead.',)].

xarray/tests/test_variable.py:1763: Failed ----------------------------------------------------------------------------------------------- Captured stderr call ----------------------------------------------------------------------------------------------- /home/karel/working/xarray/xarray/tests/test_variable.py:1763: FutureWarning: Coordinate has been deprecated. Use IndexVariable instead. x = Coordinate('x', [1, 2, 3]) ```

I'm trying to parallelize my code using Dask. Using their distributed.Client() I was able to do computations in parallel. Unfortunately, it seems ~60% of the time is spend in a file lock. As I'm only reading data and doing computations in memory, I should be able to work without a lock, so I tried to pass lock=False to open_dataset. Unfortunately this crashes my code. A minimal reproducible example can be found below:

``` python import xarray as xr import dask.array as da from dask.distributed import Client from IPython import embed

First generate a file with random numbers

rng = da.random.RandomState() shape = (10, 10000) chunks = (10, 10) dims = ['y', 'z'] x = rng.standard_normal(shape, chunks=chunks) da = xr.DataArray(x, dims=dims, name='x') da.to_netcdf('test.nc')

Open file without a lock

client = Client(processes=False) ds = xr.open_dataset('test.nc', chunks=dict(zip(dims, chunks)), lock=False)

This will crash!

print((ds['x'] * ds['x']).compute()) Crashes with (sometimes) python distributed.worker - WARNING - Compute Failed Function: getter args: (ImplicitToExplicitIndexingAdapter(array=CopyOnWriteArray(array=LazilyOuterIndexedArray(array=<xarray.backends.netCDF4_.NetCDF4ArrayWrapper object at 0x7ffb69033c50>, key=BasicIndexer((slice(None, None, None), slice(None, None, None)))))), (slice(0, 10, None), slice(5710, 5720, None))) kwargs: {} Exception: RuntimeError('NetCDF: HDF error',) `` And usually just withterminated by signal SIGSEGV (Address boundary error)`

Output of xr.show_versions()

A "Minimal, Complete and Verifiable Example" will make it much easier for maintainers to help you: http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports

```python

Your code here

```

Problem description

[this should explain why the current behavior is a problem and why the expected output is a better solution.]

Expected Output

Output of xr.show_versions()