Currently, you can back up any particular app instance (grain) by clicking "download backup" in the topbar -- this gives you a .zip of its data, which you can then re-upload to any Sandstorm server. For full-system backups, you'll need to use a standard Linux filesystem backup solution, configured outside of Sandstorm. We (Sandstorm team) plan to add the ability to configure full-system backup through the Sandstorm UI in the future. (Of course, if you use our managed hosting, we are making daily backups.)