I am copying my post from another thread, since this seems to be coming up. Disk Utility shows a single volume for the Fusion Drive, not the SSD and the HD. When highlighting the first Macintosh HD in the list, it shows Type: Logical Volume Group. When highlighting the second Macintosh HD in the list, it shows this: Using iStat Menu's Disk Activity, it shows that there are two separate disks: They would appear to be a Samsung 128GB SSD and a Hitachi 5400RPM HD. You CAN use USB 3.0 and FireWire 800 hard drives on the 2012 Mac mini (I am using them now), you just can't add them to the Fusion Drive logical volume.