'Manage an existing volume in the ZFSSA backend.
:param volume: Reference to the new volume.
:param existing_ref: Reference to the existing volume to be managed.'

def manage_existing(self, volume, existing_ref):

    lcfg = self.configuration
    existing_vol = self._get_existing_vol(existing_ref)
    self._verify_volume_to_manage(existing_vol)
    new_vol_name = volume['name']
    try:
        self.zfssa.set_lun_props(lcfg.zfssa_pool, lcfg.zfssa_project, existing_vol['name'], name=new_vol_name, schema={'custom:cinder_managed': True})
    except exception.VolumeBackendAPIException:
        with excutils.save_and_reraise_exception():
            LOG.error('Failed    to    rename    volume    %(existing)s    to    %(new)s.    Volume    manage    failed.', {'existing': existing_vol['name'], 'new': new_vol_name})
    return None
