With all these depressing threads about dying N900s, lack of Nokia stock to replace them, bulk buyers on eBay and the lack of credible N900 replacement devices in the market, I've decided that I will be using the N900 for at least another year, more likely two or three years until a whole new generation of devices is upon us.

I've just taken the plunge and bought myself a spare N900 off eBay, with a credible one month usage history, box and accessories, all for the sum of £135 delivered. Cheaper than insurance, cheaper than a new contract for a handset I probably didn't want, and if it means I can go SIM-free when the current contract is up, it'll pay for itself pretty darn quick. So now the question is how best to achieve (and then to automate) "bare-metal" redundancy against loss or failure of my primary phone; I'd like to know what others are already doing about this and whether there is a preferred approach. I'm broadly familiar with backupmenu, rsync, rdiff-backup, and so on and won't have problems backing up the FAT partitions over rsync or similar.

What I'd really like to be able to do is to fully automate a proper rootfs + optfs backup, like backupmenu takes, on a regular basis, without my having to actually boot into backupmenu and do so manually on a daily or weekly basis. Is there some way of doing a backup run at boot time, either from an initrd before the rootfs gets mounted, or with rootfs mounted read-only? Or is there a way of making it part of the shutdown process, perhaps by loading a rescue OS into RAM, chrooting to it and taking the backups from there?

If I can do either of the above, and ensure that the backup happens only if the phone is on charge, I can schedule a nightly reboot of the phone to dump the rootfs + optfs backup onto the microSD card, THEN take an incremental backup of something that actually might let me restore the phone. Does anyone already do something like this?