I performed a clean install on a late 2012 iMac with Fusion Drive using Internet recovery. Everything seems OK and the computer appears to boot and run OS X off the SSD, but when I run "diskutil list" in the terminal, it shows the SSD listed as disk1, and the HDD as disk0. This is in the reverse order that the computer came from the factory. An Ars Technica article shows the SSD as disk0 as well. http://arstechnica.com/apple/2012/11/fusion-drive-quick-look-our-predictions-confirmed/ Can anyone explain why this reversal happened and whether it's anything to be worried about? Should the boot drive always be disk0? I didn't mess with any of this manually, I just let the installer do its thing. Is there anyone else with a genuine Fusion Drive that can run diskutil list in the terminal and let me know what they get? Thanks! UPDATE: After shutting down and rebooting the computer, the SSD is now reported as disk0. After googling I found a bunch of evidence that disk ordering can change quite randomly - this is completely independent of Fusion Drive. It appears to just depend on which drive is initialised first on boot. So it literally can change from one day to the next. I wonder if anyone here is knowledgable about this stuff and can back this explanation.