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Comment by seiji | Hacker News Reader

The OS knows about entire applications / resource bundles / documents and can run stronger heuristics against your usage than a blind block-level controller.

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I would be willing to bet a fair amount of money that all of those fancy heuristics would be easily beaten in almost every case by a simple adaptive cache which was based on how often and recently sectors on the disk were accessed. The disk drive knows more about the actual data layout on the platters than the OS does, and that's what really matters here.

Over time, you are probably right. I think an OS-driven approach could have quicker time-to-steady-state resolution though.

If you have a large document (a few hundred MB) in an editor, the HD may SSDize parts of the document over and over again until the entire document is moved/cached. An OS-driven approach could move the entire document in one go.

Fusion Drive is just flashcache with some sort of adaptive caching algo. There's zero reason to care about what the type of a file is. The reason they showed it like that in the keynote was because normal people don't know what a block device is.

Feel free to buy me a shiny new 27" iMac and I'll report back how their hybrid drive implementation works in excruciating detail.

You are not correct, it is _not_ a cache but instead something that provides the union of storage between two drives. Remember, the examples have stuff _only_ on the SSD.

Instead, this appears to be an implementation of so-called "tiered storage". This is novel in that is the first time such an approach has been applied to consumer grade solutions. Usually, one might find tiered storage as part of an extremely expensive solution that EMC might give you as part of an elaborate storage system.

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