Reusing iMac Fusion Drive as external drive
you can put the old fusion drive in a usb enclosure then you should be able to boot to it by pressing the Option key when the boot chime rings. you can also use the drive in the enclosure to setup a new Mac. Using Migration Assistant you can import your entire old file system just as if you were using a Time Machine backup. The question of what to do with the drive AFTER you successfully accomplished moving your old file/apps/etc to the new Mac. All of a sudden you've got a 1.12TB or bigger drive on your hands. On Disk Utility it will show up as Fusion Drive and having the Core system with 2 partitions. I'm not sure if you can actually format the Fustion Drive as one unit and use the entire thing for whatever you wanted, like storing all your media files to be streamed from anywhere in the house.