the usb ports on the wiiu are very low powered, so you'll need a self-powered usb hub. this will provide the power required to your hard drive. alternatively you can use a y-cable, which will draw power from both usb ports on the back of the wiiu and provide enough power to your hdd. however this is not a good solution if you use a usb ethernet adapter as the y-cable will take up both ports for your hard drive.