I like to keep at least a 6-month backup offsite (in my bank safe deposit box) in case of a serious disaster. Can I use Time Machine with two different HD's? Can I have Time Machine get a backup current on HD1 and then take it to the safe deposit box? Then day-to-day use HD2 with Time Machine? Then a few months out, take HD2 to the safe deposit box and bring back HD1 for day-to-day use? Or is this going to confuse Time Machine? I know that with a laptop, when your HD is not connected, the system keeps track of what files were added or changed since the last backup. Will Time Machine compare the current system to what is on the HD, or is it simply what was changed since the last backup?