The total number of stored bytes of data for the array. This
        includes storage required for configuration metadata and user
        attributes.

def nbytes_stored(self):
        """The total number of stored bytes of data for the array. This
        includes storage required for configuration metadata and user
        attributes."""
        m = getsize(self._store, self._path)
        if self._chunk_store is None:
            return m
        else:
            n = getsize(self._chunk_store, self._path)
            if m < 0 or n < 0:
                return -1
            else:
                return m + n