code: def save(self, fname=None, link_copy=False,raiseError=False):
          
          if fname is None:
              fname = self.filename
          assert fname is not None
          save(fname, self, link_copy=link_copy,raiseError=raiseError)
docs: link_copy: only works in hfd5 format
              save space by creating link when identical arrays are found,
              it may slows down the saving (3 or 4 folds) but saves space
              when saving different dataset together (since it does not duplicate
              arrays)