Why is writing direct to Unity Catalog Volume slower than to Azure Blob Storage (xarray -> zarr)

[songhan89]

Hi,

I have some workloads whereby i need to export an xarray object to a Zarr store.

My UC volume is using ADLS.

I tried to run a simple benchmark and found that UC Volume is considerably slower.

a) Using a fsspec ADLS store pointing to the same container behind UC Volume. Result : 42 s.

b) Treat UC Volume as a LocalStore. Result : 93 s.

Does UC Volume support async I/O ? I am suspecting that this could be the reason behind the slower performance ?

import xarray as xr
import adlfs
import zarr
from zarr.storage import FsspecStore

fs = adlfs.AzureBlobFileSystem(account_name=ABS_ACCOUNT_NAME, credential=SILVER_SAS_TOKEN, asynchronous=True)

files = glob('./samples/N1S*01')

args_cubed = {'engine': 'cfgrib',
    'filter_by_keys': {
        'dataType': 'fc',
        'typeOfLevel': ['surface', 'isobaricInhPa']
        },
    'chunks': {}
 }

def preprocess(ds):
    return ds.expand_dims(['time', 'step'])

ds = xr.open_mfdataset(
    files,
    preprocess=preprocess,
    parallel=True,
    **args_cubed
)

ds2 = ds.load()

store_azb = FsspecStore(fs, path='silver/nwp/azb_benchmark_v3.zarr')
store_uc = zarr.storage.LocalStore('/Volumes/mss-uc/silver/silver-volume/nwp/unity_catalog_benchmark_v3.zarr')