def METHOD_NAME(self, user, volumes):
    vols = set()
    for k, v in self._options.items():
        if k.startswith("mountbroker-geo-replication.") \
           and user == k.split(".")[-1]:
            vols.update(v.split(","))
    vols.update(volumes)
    self.set_opt("mountbroker-geo-replication.%s" % user,
                 ",".join(vols))