Well, I guess a couple of possibilities. One is to take the SD card out and put it in another computer to see how it reads. You can use the My Computer, right click on the icon for the card and select properties. It will show the type and filesystem in the dialog box.

The second is to just jam a buttload of files on the card and see when it blows up. So create a directory of 15,000-20,000 files and sync it to the drive. If it coughs, then there is the answer.