Prince AKR

I used a Cruzer Glide 32GB for a bit, worked well enough. It will become obsolete fast if you download a lot of games. Also the constant writing to it will kill it pretty fast.

I've seen a few people around the net refute that claim, stating that while there is a maximum read/write limit, it takes eons to actually fill it up. Can anyone second that?

Because it isn't technically a supported solution, more of a work around. Games will not boot from an SD card in the Wii U, with a cheap adapter people have said the Wii U recognizes it as HDD unit of some sort but I still would go with what Nintendo suggests to use. If you ever run into problems technically and need support from Nintendo, I don't think they would be as helpful knowing you didn't follow suggested guidelines.

 

http://www.nintendol..._off_an_sd_card

I get what you're saying. I'll play around with it for a while. I've already played a few titles from it, and the games are saving just fine. So far, so good.

I don't think that is a good solution at all.

 

From Nintendo,

I'm aware that they can be used for those operations. In fact I've done all of those already (I've had my Wii U since 2012, lol).  I was just wondering if it was really all that dangerous to use it as full expandable storage. Like I said; they warned against USB Flash Drives, but not SD Cards. You said you don't think it's a good solution—any particular reason?

It might need to be formatted (or is damaged)? Temporarily sacrifice a second drive, make sure the Wii U reformats it, then copy everything over to reformat the first drive. You can also then see if large files will work on the other drive when they don't work on the preferred drive.

How was it formatted? If it's FAT32, you'll need to reformat it as NTFS.

If the drive is getting enough power and is formatted correctly, you might have a hardware problem with the drive itself - even if the PC could use it.

Alright. I'll fetch my SD Card+USB Reader and send everything that's currently on the drive to that, and then I'll try re-formatting the HDD. It works fine with my PC, although I can't remember if it was done in FAT32. It was also working great with my Wii, which I was originally using it on. 

Alright. I'll fetch my SD Card+USB Reader and send everything that's currently on the drive to that, and then I'll try re-formatting the HDD. It works fine with my PC, although I can't remember if it was done in FAT32. It was also working great with my Wii, which I was originally using it on. 

UPDATE: Yep, this is done.
I went ahead and formatted it through the Wii U first, but my MK8 save data still won't copy over. I then moved the HDD to my PC and formatted it there. I also ran a Disk Check to search for errors and bad sectors. That operation found a few bugs, which lead me to think that maybe that's what the problem was. Unfortunately, that was not the case.
 

I just moved the HDD back to the Wii U, and it formatted it just fine. I tried copying the save data over to the HDD AGAIN—and I was met with an error 3 minutes later. It's pretty much official now: my drive is partially incompatible with the Wii U. Not sure why:  it's self-powered, USB 2.0, and is able to transfer files under 1GB between the system memory and itself. I just sent over 5GBs of data from the HDD to the SD Card I talked about earlier and that went FINE. Strange situation, indeed...

If it's a USB 3.0 drive, you'll need a Y-cable to power the thing with the Wii U, it only has USB 2.0 ports.

No, it's a USB 2.0 drive. Plus, it uses AC power.