[ryannielsen]

The whole "it's not a cache" thing is a canard. Doing it right means doing it much like swap: you may have dupes in certain cases. Going beyond that actually hurts performance.

It's fundamentally not a cache. If it were a cache, Fusion Drive would not increase the total storage space. Anandtech[1] seems to confirm this, noting that Fusion Drive creates a 4GB write buffer on the SSD and all read operations will influence a pinning algorithm which will move, not cache, frequently accessed files from the HDD onto the SSD.

ReadyBoost is exactly a cache, as is ZFS's ARC and L2ARC.

Now then, regarding the statement you question… yes, it is incorrect. ReadyBoost and L2ARC are pre-existing examples of "hybrid models of blending SSD and mechanical disks" that "integrate with the OS" and do so quite intelligently. You are correct to call out that statement. But it really does appear that Fusion Drive is not a cache, but a true unioning of SSDs and HDDs managed by the OS to ensure hot files are on the SSD whenever possible.

[1] http://www.anandtech.com/show/6406/understanding-apples-fusi...

[rhplus]

The hybrid drive feature in Vista was ReadyDrive, not ReadyBoost. It never took off due to lack of driver support from manufacturers and/or Microsoft. Even so, you're right that techically it's a cache because copies are stored on both physical drives backing the logical one. I just wanted to point out that ReadyBoost was about using additional drives to use as caches, while ReadyDrive was about using hybrid drives.

http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive

http://msdn.microsoft.com/en-us/library/windows/hardware/gg4...

[BitMastro]

It looks to me more like a smart UnionFS. Clever!