You can do that with ZFS as well but that still doesn't make snapshots a backup. The backup is when you send those snapshots to a remote volume. If a backup isn't stored remotely it isn't a backup (it also shouldn't be mounted locally).
Yup, aware what ZFS could do. I was not going to suggest it since they are talking about a personal git server. ZFS likes memory, lots of it. Rsnapshot is a simple perl script that uses rsync. The backups and snapshots are wherever you point it to. Local, remote, both, 20 other locations if you are so inclined.