I need to extend my iMAC HD. I do not think I can open it and upgrade the HD inside. What I am think about is getting a Firewire 800 external HD. Does there a HD so I can connect it to MAC. it will fall sleep or turn off when Mac is power off and when MAC is power on(Firewire has power) then the HD will wake up auto. I did a lot search but no luck yet. Thanks for any information.