Backing up External drive to Time Machine - what if it's not connected? I have 2 x 1 TB drive that I use interchangeably. 1 holds Video and the other Photos. I only have 1 connected when I'm working (using Premiere or Lightroom). I have a 2 TB NAS for making redundant copy of the other 2 drives.So far I've been doing the copying manually. 

I'm considering of using Time Machine to make proper backup sets (though I'm always only interested in the latest set). I know that I can set Time Machine to backup to NAS over the network and include any external drives connected to the mac at the time.

QUestion now is:


Will Time Machine "craps out" if it can't find the external drive?
Does Time Machine handle backing up the external drives - one at a time - only when it's connected - without thinking the files/volume had been deleted?
I also have my external HDD connected from time to time. To answer to Afmrak, Time Machine only prepares (stashes) backups once it finds out you connected your Time Machine HDD. So if you haven't connected your HDD for some time, it will take a while for Time Machine to prepare and make backup.
I have never been backing up external volumes.