I don't have any time to play today, but I'll try plugging in a USB Memory Stick and an external drive. However, it may well be that the USB interface is only for keyboard and mouse.

Hardware documentation should specify it somewhere.

In particular, I'll load a linux partition and see if it can do anything - oops, no partition with it's own hardware device without an HMC, and my "private" system uses IVM, not an HMC.

I'll have to try to free up the second disk and install Linux in native mode, and see if it can communicate with various USB devices.

I haven't tried it, but I am curious about the reply cfgmgr gives.

It should see the device, but might say it does not have a driver.