So they seem to be trying to differentiate this from a typical HHD (besides the fact that it's two separate devices) by saying it's "not a cache", but practically speaking, are the benefits of "not duplicating" really worth it? Sure, you get 12.5% more space that way, but it seems like the performance implications would be almost exclusively negative.<p>On a typical HHD, under typical circumstances, all writes go to the SSD, and are copied to the HDD later on. So far so good; Apple's solution will do the same thing. And stuff being read gets copied to the SSD in both cases. Also great.<p>Now, suppose a file is loaded to the SSD and we never write to it. Now the SSD gets full, and the file has to be moved off of the SSD to make room. On a typical HHD, all that happens is the file gets deleted from the SSD. It's still on the HDD, so no further action is necessary. But on Apple's Fusion Drive, this file will have to be copied <i>back</i> to the HDD.<p>Considering that some of the largest kinds of files (e.g. videos) are exactly the sort of thing you will want to put on the SSD and not modify, this seems like a pretty terrible idea.
"There are other hybrid models of blending SSD and mechanical disks to save money, but none of them are able to integrate with the OS and do it as intelligently as Apple is able to with Fusion Drive."<p>Seriously? Aside from hybrid drives, Windows has had a very similar technology since Vista (SSD's weren't as inexpensive back then, so it wasn't terribly well received), and of course there is ZFS with it's L2ARC.<p>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.
I wonder if they can do a write log to the spinning rust (sequential write, pretty fast, slow on the SSD) and then periodically resolve the deltas. I played around briefly with a system which put metadata in a RAM disk (battery backed up to SSD) and actual data blocks on the disk. There was a huge benefit in that system of splitting the metadata i/o's from the read/write I/Os, really helped overall performance. I look forward to seeing the whitepaper on this tech if they publish it.
Seems like an interesting choice not use the fast disk as a cache. This is the design that Windows 7 and beyond went with. <a href="http://technet.microsoft.com/en-us/magazine/ff356869.aspx" rel="nofollow">http://technet.microsoft.com/en-us/magazine/ff356869.aspx</a>
I think its funny how Apple tries to solve its file system issues with SSDs. No other popular file system will get quite as unbearably slow when in heavy use as HFS+. No other file system will just randomly create errors and little corruptions here and there in regular use. No other popular OS will come to a complete halt as soon as it starts swapping because its file system can't handle it.<p>And instead of fixing that stuff, Apple is pushing SSDs to everyone. Way of the future.
It's the poor man's (or rather consumer's) 3PAR!<p>HP 3PAR, StorSimple etc all have done it long time back but at a bigger scale. Apple is just scaling it down, and bringing it in front of the regular Joe (as regular as Apple customers tend to be) in a non-complex manner.
Reminds me of Seagate's Momentus XT, except it sounds like the file management is done in the OS and not on the drive, and that the SSD is not being used as a cache.<p><a href="http://www.anandtech.com/show/3734/seagates-momentus-xt-review-finally-a-good-hybrid-hdd" rel="nofollow">http://www.anandtech.com/show/3734/seagates-momentus-xt-revi...</a><p>I'm guessing the SSD portion will be MLC?<p>Are there any other hybrid drives like this in the wild?
I wonder if this was implemented as a combination of LVM with an extended area for the Hot File Clustering [1], which currently reserves only 0.5% spinning boot disks for small files with a high temperature. Lots to speculate about, little to know at this point, it seems.<p>[1] <a href="http://osxbook.com/book/bonus/misc/optimizations/#THREE" rel="nofollow">http://osxbook.com/book/bonus/misc/optimizations/#THREE</a>
This is really cool tech. Not only does it solve the problem of "having more stuff than I can fit on an SSD I can afford" but "long-term storage that I still need periodic random access to but I/O performance is not paramount, but heavens no, it needs to be faster than a tape backup"
I wonder if it's this: <a href="http://en.wikipedia.org/wiki/Smart_Response_Technology" rel="nofollow">http://en.wikipedia.org/wiki/Smart_Response_Technology</a><p>Oh, it's probably not, because that page says the maximum size is 64GB.<p>(I work @ Intel and have no inside knowledge about this feature at all.)