This is somehow similar to rsnapshot, just the directory layout is different:
<backup_set>/<snapshot_id>/...
e.g.:
server1/0/...
server1/1/...
server1/2/...
server1/3/...
server2/0/...
server2/1/...
...
In the directories 0..N, there is a file BACKUP_TIMESTAMP that contains date tool output.