'Return an appropriate backup service host.'

def _get_available_backup_service_host(self, host, az):

    backup_host = None
    if ((not host) or (not CONF.backup_use_same_host)):
        backup_host = self._get_any_available_backup_service(az)
    elif self._is_backup_service_enabled(az, host):
        backup_host = host
    if (not backup_host):
        raise exception.ServiceNotFound(service_id='cinder-backup')
    return backup_host
