diff --git a/odc/loader/test_memreader.py b/odc/loader/test_memreader.py
index 8ff6a97..b769ec4 100644
--- a/odc/loader/test_memreader.py
+++ b/odc/loader/test_memreader.py
@@ -4,30 +4,40 @@
 
 from __future__ import annotations
 
+import json
+
 import numpy as np
+import pytest
 import xarray as xr
 from odc.geo.data import country_geom
 from odc.geo.geobox import GeoBox
-from odc.geo.xr import ODCExtensionDa, rasterize
+from odc.geo.xr import ODCExtensionDa, ODCExtensionDs, rasterize
 
-from .testing.mem_reader import XrMemReader, XrMemReaderDriver, raster_group_md
+from .testing.mem_reader import Context, XrMemReader, XrMemReaderDriver, raster_group_md
 from .types import FixedCoord, RasterGroupMetadata, RasterLoadParams, RasterSource
 
 # pylint: disable=missing-function-docstring,use-implicit-booleaness-not-comparison
-# pylint: disable=too-many-locals,too-many-statements
-
+# pylint: disable=too-many-locals,too-many-statements,redefined-outer-name
 
-def test_mem_reader() -> None:
-    fake_item = object()
 
+@pytest.fixture
+def sample_ds() -> xr.Dataset:
     poly = country_geom("AUS", 3857)
     gbox = GeoBox.from_geopolygon(poly, resolution=10_000)
     xx = rasterize(poly, gbox).astype("int16")
     xx.attrs["units"] = "uu"
     xx.attrs["nodata"] = -33
 
-    ds = xx.to_dataset(name="xx")
-    driver = XrMemReaderDriver(ds)
+    return xx.to_dataset(name="xx")
+
+
+def test_mem_reader(sample_ds: xr.Dataset) -> None:
+    fake_item = object()
+
+    assert isinstance(sample_ds.odc, ODCExtensionDs)
+    gbox = sample_ds.odc.geobox
+    assert gbox is not None
+    driver = XrMemReaderDriver(sample_ds)
 
     assert driver.md_parser is not None
 
@@ -43,6 +53,8 @@ def test_mem_reader() -> None:
     assert md.extra_dims == {}
     assert md.extra_coords == []
 
+    ds = sample_ds.copy()
+    xx = ds.xx
     yy = xx.astype("uint8", keep_attrs=False).rename("yy")
     yy = yy.expand_dims("band", 2)
     yy = xr.concat([yy, yy + 1, yy + 2], "band").assign_coords(band=["r", "g", "b"])
@@ -149,3 +161,35 @@ def test_raster_group_md():
     assert rgm.extra_dims_full() == {"band": 3}
     assert len(rgm.extra_coords) == 1
     assert rgm.extra_coords[0] == coord
+
+
+def test_memreader_zarr(sample_ds: xr.Dataset):
+    assert isinstance(sample_ds.odc, ODCExtensionDs)
+    assert "xx" in sample_ds
+
+    gbox = sample_ds.odc.geobox
+    chunks = None
+
+    md_store = {}
+    chunk_store = {}
+    sample_ds.to_zarr(md_store, chunk_store, compute=False, consolidated=True)
+
+    assert ".zmetadata" in md_store
+    zmd = json.loads(md_store[".zmetadata"])["metadata"]
+
+    src = RasterSource(
+        "file:///tmp/no-such-dir/xx.zarr",
+        subdataset="xx",
+        driver_data=zmd,
+    )
+    assert src.driver_data is zmd
+
+    cfg = RasterLoadParams.same_as(src)
+
+    ctx = Context(gbox, chunks)
+    rdr = XrMemReader(src, ctx)
+
+    roi, xx = rdr.read(cfg, gbox)
+    assert isinstance(xx, np.ndarray)
+    assert xx.shape == gbox[roi].shape.yx
+    assert gbox == gbox[roi]
diff --git a/odc/loader/testing/mem_reader.py b/odc/loader/testing/mem_reader.py
index 10d9a61..3f60c83 100644
--- a/odc/loader/testing/mem_reader.py
+++ b/odc/loader/testing/mem_reader.py
@@ -26,8 +26,15 @@
     ReaderSubsetSelection,
 )
 
+SomeDoc = dict[str, Any]
+ZarrSpec = dict[str, Any]
+ZarrSpecFs = dict[str, Any]
+
+
+def extract_zarr_spec(src: SomeDoc) -> ZarrSpecFs | None:
+    if ".zmetadata" in src:
+        return src
 
-def extract_zarr_spec(src: dict[str, Any]) -> dict[str, Any] | None:
     if "zarr:metadata" in src:
         # TODO: handle zarr:chunks for reference filesystem
         zmd = {"zarr_consolidated_format": 1, "metadata": src["zarr:metadata"]}
@@ -39,6 +46,45 @@ def extract_zarr_spec(src: dict[str, Any]) -> dict[str, Any] | None:
     return {".zmetadata": json.dumps(zmd)}
 
 
+def _from_zarr_spec(
+    spec_doc: ZarrSpecFs,
+    regen_coords: bool = False,
+    fs: fsspec.AbstractFileSystem | None = None,
+    chunks=None,
+    target: str | None = None,
+    fsspec_opts: dict[str, Any] | None = None,
+) -> xr.Dataset:
+    fsspec_opts = fsspec_opts or {}
+    rfs = fsspec.filesystem(
+        "reference", fo=spec_doc, fs=fs, target=target, **fsspec_opts
+    )
+
+    xx = xr.open_dataset(rfs.get_mapper(""), engine="zarr", mode="r", chunks=chunks)
+    gbox = xx.odc.geobox
+    if gbox is not None and regen_coords:
+        # re-gen x,y coords from geobox
+        xx = xx.assign_coords(xr_coords(gbox))
+
+    return xx
+
+
+def _resolve_src_dataset(
+    md: Any,
+    *,
+    regen_coords: bool = False,
+    fallback: xr.Dataset | None = None,
+    **kw,
+) -> xr.Dataset | None:
+    if isinstance(md, dict) and (spec_doc := extract_zarr_spec(md)) is not None:
+        return _from_zarr_spec(spec_doc, regen_coords=regen_coords, **kw)
+
+    if isinstance(md, xr.Dataset):
+        return md
+
+    # TODO: support stac items and datacube datasets
+    return fallback
+
+
 class XrMDPlugin:
     """
     Convert xarray.Dataset to RasterGroupMetadata.
@@ -57,32 +103,10 @@ def __init__(
         self._template = template
         self._src = src
 
-    def _from_zarr_spec(
-        self,
-        spec_doc: dict[str, Any],
-        regen_coords: bool = False,
-    ) -> xr.Dataset:
-        rfs = fsspec.filesystem("reference", fo=spec_doc)
-        xx = xr.open_dataset(rfs.get_mapper(""), engine="zarr")
-        gbox = xx.odc.geobox
-        if gbox is not None and regen_coords:
-            # re-gen x,y coords from geobox
-            xx = xx.assign_coords(xr_coords(gbox))
-
-        return xx
-
     def _resolve_src(self, md: Any, regen_coords: bool = False) -> xr.Dataset | None:
-        src = self._src
-
-        if isinstance(md, dict) and (spec_doc := extract_zarr_spec(md)) is not None:
-            src = self._from_zarr_spec(spec_doc, regen_coords=regen_coords)
-
-        if isinstance(md, xr.Dataset):
-            src = md
-
-        # TODO: support stac items and datacube datasets
-
-        return src
+        return _resolve_src_dataset(
+            md, regen_coords=regen_coords, fallback=self._src, chunks={}
+        )
 
     def extract(self, md: Any) -> RasterGroupMetadata:
         """Fixed description of src dataset."""
@@ -94,20 +118,27 @@ def extract(self, md: Any) -> RasterGroupMetadata:
 
         return self._template
 
-    def driver_data(self, md: Any, band_key: BandKey) -> xr.DataArray | None:
+    def driver_data(
+        self, md: Any, band_key: BandKey
+    ) -> xr.DataArray | ZarrSpec | ZarrSpecFs | SomeDoc | None:
         """
         Extract driver specific data for a given band.
         """
         name, _ = band_key
 
+        if isinstance(md, dict):
+            if (spec_doc := extract_zarr_spec(md)) is not None:
+                return spec_doc
+            return md
+
         if isinstance(md, xr.DataArray):
             return md
 
-        if (src := self._resolve_src(md, regen_coords=True)) is not None:
-            if (aa := src.data_vars.get(name)) is not None:
-                return aa
+        src = self._resolve_src(md, regen_coords=False)
+        if src is None or name not in src.data_vars:
+            return None
 
-        return None
+        return src.data_vars[name]
 
 
 class Context:
@@ -136,8 +167,48 @@ class XrMemReader:
     # pylint: disable=too-few-public-methods
 
     def __init__(self, src: RasterSource, ctx: Context) -> None:
-        self._xx: xr.DataArray = src.driver_data
+        driver_data: xr.DataArray | xr.Dataset | SomeDoc = src.driver_data
+        self._spec: ZarrSpecFs | None = None
+        self._xx: xr.DataArray | None = None
         self._ctx = ctx
+        self._src = src
+
+        if isinstance(driver_data, xr.DataArray):
+            self._xx = driver_data
+        elif isinstance(driver_data, xr.Dataset):
+            subdataset = src.subdataset
+            assert subdataset in driver_data.data_vars
+            self._xx = driver_data.data_vars[subdataset]
+        elif isinstance(driver_data, dict):
+            self._spec = extract_zarr_spec(driver_data)
+        elif driver_data is not None:
+            raise ValueError(f"Unsupported driver data type: {type(driver_data)}")
+
+        assert driver_data is None or (self._spec is not None or self._xx is not None)
+
+    def _resolve_data_array(self) -> xr.DataArray:
+        if self._xx is not None:
+            return self._xx
+
+        assert self._spec is not None
+        kw = {
+            "target": self._src.uri,
+            "chunks": self._ctx.chunks,
+        }
+        src_ds = _from_zarr_spec(self._spec, regen_coords=True, **kw)
+
+        if src_ds is None:
+            raise ValueError("Failed to interpret driver data")
+
+        subdataset = self._src.subdataset
+        if subdataset is None:
+            _first, *_ = src_ds.data_vars
+            subdataset = str(_first)
+
+        if subdataset not in src_ds.data_vars:
+            raise ValueError(f"Band {subdataset!r} not found in dataset")
+        self._xx = src_ds.data_vars[subdataset]
+        return self._xx
 
     def read(
         self,
@@ -147,7 +218,7 @@ def read(
         dst: np.ndarray | None = None,
         selection: ReaderSubsetSelection | None = None,
     ) -> tuple[tuple[slice, slice], np.ndarray]:
-        src = self._xx
+        src = self._resolve_data_array()
 
         if selection is not None:
             # only support single extra dimension