FWIW, I have two 1T G drive mobile disks. On both my Macbook Pro and my Mac Pro, the US 2 works fine with the expected read/write speeds. When I connect using the Firewire 800 ports, the read/write speed is quite slow. The speed is comparable to the USB 2 speeds or a bit less. This happens on both computers, different cables and different computer ports. It also happens with both G drives. I called the G drive tech support and was told that the Firewire should be 2-3 times faster than the USB 2. There maybe something flaky about the G drive interface. For the record, I also use several 500GB G mini drives with Firewire 800 with the expected performance implying that problems with my computers is less likely than some issue with the mobile drives.