'Pick up least used pool.'

def _select_leastused_poolnumber(self, volume, pools, xml, option=None):

    size = (volume.size * units.Gi)
    pools = [pool for (pn, pool) in pools.items() if ((pool['free'] >= size) and ((len(self._properties['pool_pools']) == 0) or (pn in self._properties['pool_pools'])))]
    return self._return_poolnumber(pools)
