How to backup USB boot drive

[psychokiller]

Hi all,
I have a few appliances around the house based on Arch Linux ARM (dockstars, now a zyxel nsa325) and I would like to make them safe to USB wear issues.

All of them boot from USB pendrives and those are doomed to fail, one day or another, it is not a matter of IF but WHEN, we all know this here right?

So the question is: what is the best strategy to have a second pendrive in every box that constantly mirrors (even daily, not necessarily continuously) the boot drive and can be swapped and boot from it if the first one fails?
- LVM snapshots?
- any obscure sync utility like, as an example rsnapshot?
- a simple dd from boot drive to the second drive in a cron job?

How can consistency be guaranteed?

Anyone willing to suggest how to approach this issue will have may eternal gratitude, and maybe even a more tangible reward

TIA, Paolo

[summers]

Use cron and rsync. Rsync will just copy the differences, so it will save ware on the usb. Also see it you can make regularly written directories as tmpfs, so they only get written to ram and not to flash/usb.

[psychokiller]

I am still looking for a good solution: the real problem with rsync is consistency.
Everything read/write and open might be corrupted... or maybe not?
Have to check how rsync handles open files.
Paolo