I have a 2Tb USB powered xtnal HDD connected to my Airport Extreme to use as a Time Capsule backup drive. No problems at all, it all works as it should but I wondered if leaving the usb powered hdd connected permanently, i.e always on, would it be detrimental to the airport device or the drive itself?? I'm thinking, too much load for the airport power supply? or reliability long term of the drive.....