Best way to keep Time Capsule and external drive in sync?

[PatriotInvasion]

So I have a 13" rMBP that backs up all of it's contents to a Time Capsule. I also have an external 1TB HDD that has files I cannot fit on my MBP's small 128GB SSD.

I'd like Time Machine to backup BOTH my rMBP's drive and the external drive to the Time Capsule. This can happen by removing the external drive from Time Machine's exclude list, but there's a catch.. If the external is not connected, Time Machine backs up just the rMBP and then the next time the external is connected, Time Machine backs up the entire external drive to the Time Capsule again (likely because it did not find it in the most recent backup)!

Any idea of a better way to backup a Mac+External drive to a Time Capsule when the external isn't always plugged in to the Mac?

 

[ColdCase]

Time machine (mountain lion) does not seem to give me an option to remove a SD card or external drive from the exclude list. I use Carbon Copy Cloner to back up "external" drives. If the drive is not there an notification pops up and you can chose to defer or skip which will close the window. CCC will detect the mounting of the external drive and automatically initiate back up. Same with the drive you are backing up to.

 

[PatriotInvasion]

Time machine (mountain lion) does not seem to give me an option to remove a SD card or external drive from the exclude list. I use Carbon Copy Cloner to back up "external" drives. If the drive is not there an notification pops up and you can chose to defer or skip which will close the window. CCC will detect the mounting of the external drive and automatically initiate back up. Same with the drive you are backing up to.

You will not be able to remove any drive from Time Machine's "exclude" list that is not formatted as Mac OS Extended (Journaled).

Lucky, mine is formatted that way. My issue is that because the external drive isn't connected to my rMBP 24/7, Time Machine thinks the external is something new every time it tries to back it up (because the external was not present during the most recent backup), and thus backs up the entire drive in full.

Seems like my only solution is to turn off automatic backups, and manually run a backup to my Time Capsule ONLY when the external is indeed connected. This avoids the situation where the most recent backup does not contain the external drive. Unfortunately, this takes away a huge benefit of Time Machine --- automatic backups that you don't need to think about