'Creates a consistency group snapshot out of one or more flexvols.
ONTAP requires an invocation of cg-start to first fence off the
flexvols to be included in the snapshot. If cg-start returns
success, a cg-commit must be executed to finalized the snapshot and
unfence the flexvols.'

def create_cg_snapshot(self, volume_names, snapshot_name):

    cg_id = self._start_cg_snapshot(volume_names, snapshot_name)
    if (not cg_id):
        msg = _('Could    not    start    consistency    group    snapshot    %s.')
        raise exception.VolumeBackendAPIException(data=(msg % snapshot_name))
    self._commit_cg_snapshot(cg_id)
