'Pick up backup pool for DDR.'

def _select_ddr_poolnumber(self, volume, pools, xml, option):

    size = (option * units.Gi)
    pools = [pool for (pn, pool) in pools.items() if ((pool['free'] >= size) and (pn in self._properties['pool_backup_pools']))]
    return self._return_poolnumber(pools)
