code: def nbytes_stored(self):
          
          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
docs: The total number of stored bytes of data for the array. This
          includes storage required for configuration metadata and user
          attributes.