'Failover or back a volume pair.
:param array: the array serial number
:param device_id: the source device id
:param rdf_group: the rdf group number
:param extra_specs: extra specs
:param local_vol_state: the local volume state
:param failover: flag to indicate failover or failback -- bool'

def failover_volume(self, array, device_id, rdf_group, extra_specs, local_vol_state, failover):

    if (local_vol_state == WRITE_DISABLED):
        LOG.info('Volume    %(dev)s    is    already    failed    over.', {'dev': device_id})
        return
    if failover:
        action = 'Failing    over'
    else:
        action = 'Failing    back'
    LOG.info('%(action)s    rdf    pair:    source    device:    %(src)s    ', {'action': action, 'src': device_id})
    self.rest.modify_rdf_device_pair(array, device_id, rdf_group, extra_specs, split=False)
