LVM snapshots
I'd used LVM to set up logical volumes as per this guide on my last crunchbang install. I created root, home and swap volumes for my main distro and then later (as per Funishment post) set up similar volumes to dual-boot Arch. The snapshot bit looked beyond me at the time so I never got round to that. Now I'm confident enough to get GRML installed to USB and use that, with LVM in the command line (as opposed to the system-config-lvm gui) to follow the instructions here . So, there's not much more to say, beyond following the instructions on the thread. Initially I thought about using LVM to shrink the crunchbang root volume, which I've crazily allocated nearly 20GB after running out of space for the OS last time and having to grow it with LVM. Shat it, though. the thought of messing up the root partition while trying to find a way to back up the root partition was too scary. So I went ahead and allocated 4G to the snap volume instead of the 1G used in the example...