Ho un mezzo ricordo che l'hdd andasse formattato dal wiiu...
Confermo:
What data can be stored on a USB storage device?
Once a USB storage device has been exclusively configured for use with a Wii U console, it can be used to store games, applications, new downloadable content, application updates and save data. Once a device has been configured for use with a Wii U console, it cannot be used with another Wii U console, PC, etc., unless it is reformatted.
Why do I have to format my USB storage device?
To optimize performance and ensure a consistent experience, all USB storage devices must be formatted and configured on the Wii U console for exclusive use with the console. Once a device has been configured for use with a Wii U console, it cannot be used with another Wii U console, PC, etc., unless it is reformatted.
(nintendo.com)