Missing Blocks when loading zarr file

What happened?

Under load blocks of Zarr objects go missing. This happens on our minio server (see example) and on the hpc file system. This happens under load, when the filesystem gets slow, so I guess there must be a timeout somewhere.

What did you expect to happen?

A complete map.

Incomplete map:

Complete map, when the filesystem is not under load:

Minimal Complete Verifiable Example

# Calculate global temperature trends

from dask.distributed import Client
import xarray as xr
from scipy import stats
from datetime import datetime
import matplotlib.pyplot as plt


def slope(y):
    x = list(range(0, len(y)))
    l = stats.linregress(x, y)
    return l.slope


def main():
    print(datetime.now(), "startup", flush = True)
    print(datetime.now(), "starting dask workers", flush = True)
    Client(n_workers=1, threads_per_worker=32, memory_limit='64GB')

    print(datetime.now(), "opening esdc", flush = True)
    c = xr.open_zarr("http://data.rsc4earth.de:9000/earthsystemdatacube/v3.0.1/esdc-8d-0.25deg-256x128x128-3.0.1.zarr/")

    print(datetime.now(), "getting air teperature data", flush = True)
    ct = c.air_temperature_2m

    print(datetime.now(), "setup calculations", flush = True)
    cs = xr.apply_ufunc( 
            slope, 
            ct, 
            input_core_dims=[['time']], 
            vectorize=True, 
            dask='parallelized', 
            dask_gufunc_kwargs=dict(allow_rechunk=True))

    print(datetime.now(), "saving data", flush = True)
    csset = xr.Dataset(dict(tslope = cs))
    csset.to_zarr(store="temp_slopes.zarr", mode="w")
    print(datetime.now(), "plotting", flush = True)
    cssetcalc = xr.open_zarr("temp_slopes.zarr")
    cssetcalc.tslope.plot()
    plt.savefig("temperature_trends.png")
    print(datetime.now(), "done", flush = True)



if __name__ == '__main__':
    main()

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

This only seems to happen under load, so you will need to stress the server a bit to reproduce it.

Environment

Start by running the supplied MVCE against the example MinIO Zarr URL while stressing the filesystem, since the issue reports missing blocks only under load. Compare the resulting map with the complete map and capture logs or a traceback; done means identifying and preventing incomplete Zarr reads under slow-storage conditions.