I have a 32GB Wii U that I use exclusively for downloadable games. This was a perfectly serviceable amount of storage until last week when Lego City Undercover came out and wanted 19GB. I'd imaging that this will become more of a trend, Wii U titles coming in at greater than 10GB. I could have deleted some items and crammed Lego City on to my Wii U, but that would not have been pleasant. As such, it was time for an upgrade. My first attempt was to simply add a 1TB USB HDD to my Wii U. The process was not as smooth as it should have been, hence a thread to fill you all in on what you need to know.
This is the drive I picked up. It's an average, cheap 2.5" 1TB drive in a USB 3.0 enclosure. It ships with a USB 3.0 cable with one connector on each end. Sounds obvious, right, so why am I telling you this? Well, unlike modern PCs the Wii U sticks very strictly to the USB 2.0 spec of only providing 500ma of power on each port. This isn't quite enough to spin up a laptop hard drive so you quickly run in to a power issue. Effectively the Wii U sees the drive, will format it, will write to it slowly, then read from it so slowly as to lock up any game you try to run. I believe the power-starved drive simply gets stuck in a cycle of trying to spin up repeatedly, so it appears that it almost
The solution is this:
This cable allows you to draw power from the second USB port on the back of the Wii U, giving you 1000ma total. This is enough to spin up and run modern 2.5" USB hard drives. It used to be pretty common for similar cables to come with USB 2.0 drives, before standard USB 2.0 ports on PCs started providing 1000-2000ma, but instead stuck to the official spec of 500ma. There may be drives out there that still come with these Y cables to draw power from the second port, but I don't know of any off the top of my head. The aftermarket one is cheap enough that you should just plan to add it to your HDD purchase.
As part of adding this USB HDD, I did some basic testing of the Wii U's storage speeds. Copying large games in and out from the Wii U's internal storage works out to a read/write speed of about 14.5MBps. This is roughly what the 360 manages with its USB storage at 16MBps, but slower than the 25MBps that the same HDD gets hooked up USB 2.0 to my PC. I also did some basic load tests. Loading up the Rayman Origins demo took the same 16-17 seconds whether on internal or external storage. There was a variance of about a second in favor of USB storage, but that can easily come down to me being a bit inaccurate with the stopwatch. Lego City has long loads coming from either location as well. Load speeds seem to be quick enough that I'd say it doesn't matter if you are using internal or USB storage. If I were to hazard a guess, it's rather likely that the Wii U's internal flash is the limiting factor at 14.5MBps. The USB connection probably gets closer to the 16MBps that the 360 does, but it's currently impossible to prove that out. On the other hand, flash has instant seeks, while HDD seeks have a certain amount of latency. As a sum total, it's a wash.
An additional thing to note: The Wii U handles data folders in an odd fashion. It lumps saves and game data all together in one folder, and only lets you move titles as a single unit. I would prefer if saves were kept on the Wii U while game data was kept on the USB drive. The hard drive is simply more likely to die than the Wii U is. The OS does not allow this though. It operates more like the PS3 where everything has to be on one drive, rather that like the 360 that lets you put any data wherever you want. Want some of your saves on USB flash, some other saves in the cloud, and your game data on the large internal hard drive? Sure, why not! Want to put a single game on that USB flash as well to take advantage of instant seek times? Alright, sounds good! The Xbox 360 method is more friendly to the consumer.