That's just funny and humerous :) In such a case, would two identical HDD's at software RAID 1 (which if I remember correctly is just mirroring) be good enough? OR would it be better to keep the backup/second HDD unmounted and just mount for a scripted backup?
RAID1 won't protect you from a disaster, like removing files from accident, virus corruption, corruption due to a power failure, etc. RAID1 is usually used to protect against HDD failures, not as a backup solution.
You can also use LVM snapshots as a means for creating backups from live production filesystems,
