New iMac 27 owner. Using a Fantom Greendrive with two partitions, one for TM and one for CCC. So far so good. Plan on backing up the most recent CCC clone to a portable HD every now and then. Does everyone just leave their external drive on 24/7 for TM? When people are talking about a 2 to 3 year life span for external drives, are they talking about leaving them on all the time? Additionally with this drive I can't have the iMac go to sleep (at least the computer; I have the display set to sleep).