The FAQ for the Wii U regarding external storage recommends that you use an external hard drive with a dedicated power source, but is the dedicated power source absolutely necessary? I want to know, because I have an extra external hard drive lying around that doesn't connect to an external power source, and I am wondering if it will work.
According to Nintendo support, a dedicated power source is not necessary, but recommended.
Can bus-powered hard disc drives be used with Wii U?
Some bus-powered hard disc drives draw more current than the USB 2.0 specification and might not run stably, so we cannot guarantee that such devices will run properly on Wii U without the use of a supplemental power cable called a y-cable that draws power from two USB ports. For best results, we recommend using a external storage device with its own power supply that connects to the Wii U system via the USB port on the console.
From the above quote, it appears that although the use of a y-cable is already good enough, you might still encounter a drive requiring more power than even two USB 2.0 ports together can officially provide.
To clarify definitions for my answer (as this is atleast relative to how they are packaged here, in Australia), external hard drives are the bigger units that have a dedicated power source, while portable hard drives are smaller, and power from the USB connection.
Note that Nintendo only recommend an external hard drive, and do not list it as a hard requirement.
The Wii-U can support portable hard drives, however, an external is simply more efficient.
I can think of two reasons off the top of my head.
- Not requiring the Wii-U to power the hard drive is simply one less thing it is doing. This will have an arguabley insignificant impact on performance and/or reliability.
- Generally speaking, it is easier to obtain larger hard drives in external format. Larger hard drives hold more games.