Yes, it’s true that Apple new drive setup named Fusion is NOT a Software RAID – what I’m using is a metaphor, so bare with me on this. In fact, Mac Observer’s look at the technology get’s right to the point on RAID as well as what it does:
This is not a simple RAID, however, as 100% of the “magic” is done within OS X itself. What Fusion Drive does is it watches what files and applications you run most regularly and it moves them to the SSD. It will also take stuff that you aren’t using all that often and moves it to the mechanical drive.
What this is, however, looks very similar to other software-based solutions to memory/speed/access issues. The example I use is of Microsoft’s Software RAID capabilities in Windows. While it does work, we would rather trust that process to the speedier hardware RAID controller than take a perceived performance hit by doing it inside of Windows. Almost no network administrator I know would trust a RAID subsystem to Windows (over vastly superior hardware solutions).
I don’t trust Apple to make the right “magical” choices with what drive to store “most used” applications or data and which drive to use for longer-term stuff. Trusting that may cause application or data files to “magically” disappear with little recourse or diagnostic options. With likely few third-party apps that can work with Fusion right now, and simply the Fusion-supported version of Disk Utility available to get out out of a bind; I’d be one the first Apple users to skip this option until it’s been much more well worn.
Update: In Apple, SSDs, and the Fusion Drive Ripoff, J. Glenn Kunzler argues the technology is neither new or appropriately priced.