This question doesn't seem to be addressed on the rdiff-backup site, and is the main advantage of the posted solution: How much time do you waste getting a system with a dead main disk back online?
Regardless of your backup strategy, you're going to have to replace the physical disk. If the disk you are backing up to is compatible with the broken disk, you 1) already have a disk to put in your computer, and 2) you can already boot off it. So the time wasted is the absolute minimum.
Even for people using rdiff, it's probably best to have a ready-to-go backup as described in the article. His recommendation of having a bootable backup is still valid, and is not limited to the "My house just burned down" case. That's what the third disk is for :-)
Regardless of your backup strategy, you're going to have to replace the physical disk. If the disk you are backing up to is compatible with the broken disk, you 1) already have a disk to put in your computer, and 2) you can already boot off it. So the time wasted is the absolute minimum.
Even for people using rdiff, it's probably best to have a ready-to-go backup as described in the article. His recommendation of having a bootable backup is still valid, and is not limited to the "My house just burned down" case. That's what the third disk is for :-)