'Creates a group from source.
:param ctxt: the context of the caller.
:param group: the Group object to be created.
:param volumes: a list of Volume objects in the group.
:param group_snapshot: the GroupSnapshot object as source.
:param snapshots: a list of snapshot objects in group_snapshot.
:param source_group: the Group object as source.
:param source_vols: a list of volume objects in the source_group.
:returns: model_update, volumes_model_update'

def create_group_from_src(self, ctxt, group, volumes, group_snapshot=None, snapshots=None, source_group=None, source_vols=None):

    if volume_utils.is_group_a_cg_snapshot_type(group):
        return self._create_consistencygroup_from_src(ctxt, group, volumes, group_snapshot, snapshots, source_group, source_vols)
    raise NotImplementedError()
