How to use Time Machine with newly cloned source disk?

Question

I've got an iMac (10.6.8) which I'm using with a Time Capsule and Time Machine.
Recently, the iMac's internal disk started to fail. Instead of going through the effort and expense of replacing it in a fairly old computer, I added an external FireWire disk, cloned the internal disk onto it using Carbon Copy Cloner, and then unmounted the internal disk. Now I'm running the exact same system off the external FireWire disk (with no obvious performance loss, I'm happy to say).
When Time Machine saw the new disk, it started to prepare to copy everything on it. I don't know if it was going to treat it as a separate set of backups (like a separate computer), or treat it as a massive update to all the files on the same computer.
Here's what I want to happen, in order of preference:
(1) Get Time Machine to treat the new disk as the same filesystem as the old disk, and update only the files that have changed.
(2) Have Time Machine start a new backup folder. The initial backup will be slow of course.
(3) Time Machine treats the new filesystem as continuous with the old one, but with 300GB of sudden "changes" (because all the files are "different"). This is my least preferred option.
Can anyone advise me as to what my options are, and to what Time Machine will do if left to its own devices?

Answer 1

I think that the way that Time Machine works, you will either have to go with your option (3) [inefficient from the perspective of disk space usage] or simply erase the backup drive and start anew with a new Time Machine backup process [efficient from a space usage perspective but you lose all the verisoning info from previous backups].
Time Machine will see the cloned drive as a physically different drive with lots of files that it has never backed up. I think the only way it could tell that they were the same files content wise as what you had backup up earlier would be to do a bit by bit comparison (which Time Machine does not do). I think Time Machine might look at some file meta data and there might be a way to spoof it so it thinks what you want it to think, but imagine the work required to do this for hundreds of thousands of files. Some disk clone software claims to try to do this and some have bit by bit cloning options, but Time machine will still see that external drive as a physically different (never backed up) drive from the internal one that it has backed up. It might be nice to have a Time Machine option so you could tell it what you want it to assume and do, but Time Machine has a fairly simple interface and doesn't present the user with such an option (to my knowledge).
If it were me, I would buy a new Time Machine backup drive and use that to backup the external cloned drive (now your primary drive), while saving the original Time machine backup drive as an archive with all its versioning, which provides you with additional backup redundancy and history. After some time has passed, you could eventually decide to erase that (by then, older) Time Machine backup drive and use it for some other purpose.