backing up and restoring a xen linode

The old UML linodes were easy to back up and restore – you didn't need to worry about doing anything special in order to boot. As long as the filesystem was set up properly, everything was fine.

I'm curious about how this has changed under xen. Could I just rsync a file system back into place and boot it? Or is there some sort of bootloader that has to be installed on xen linodes?