Meet Fusion Drive

Available as a build-to-order option on both the new Mac mini and the new iMac is Apple’s own take on SSD caching, Fusion Drive. In true Apple fashion there are only two Fusion Drive configurations available: 1TB and 3TB. The 1TB option is only available on the upgraded Mac mini ($799) or any of the iMacs, while the 3TB Fusion Drive is a 27-inch iMac exclusive.

In all of these cases, the Fusion Drive is a combination of a 1TB or 3TB hard drive (2.5” or 3.5”) and a 128GB Samsung PM830 based SSD. In the Mac minis this SSD is a 2.5” drive, while in the iMacs it’s the same custom interface that’s used in the MacBook Air and MacBook Pro with Retina Display. For my testing I used a 1TB Fusion Drive in a 27-inch iMac.

Fusion Drive Options
  Mac mini (2012) Mac mini (2012) Mac mini server (2012) 21.5-inch iMac (2012) 27-inch iMac (2012)
Base System Cost $599 $799 $999 $1299/$1499 $1799/$1999
1TB Fusion Drive - +$250 - +$250 +$250
3TB Fusion Drive - - - - +$400
Largest Standalone SSD - 256GB
(+$300)
2x256GB
(+$600)
- 768GB
(+$1300)

The size of the SSD used in Apple’s Fusion Drive is much larger than what we usually find in a caching setup. Most OEMs ship with 8 - 24GB of NAND, and even then the drives rarely use a good controller. In the case of Apple’s Fusion Drive, Samsung’s PM830 continues to be one of the best combinations of performance and reliability we’ve ever tested. While I would’ve personally picked something like the Link A Media or Intel S3700 controller due to their excellent performance consistency, the PM830 is probably a more proven and/or affordable option for Apple.

Right off the bat Fusion Drive is different than most of the hybrid/caching solutions we’ve seen, but where it really diverges from the norm is in the software component. This isn’t simply Intel’s Smart Response Technology running under an Apple brand, instead we’re looking at virtualized storage courtesy of OS X’s Core Storage. First introduced in Lion, Core Storage is a logical volume manager that allows the OS to treat multiple physical disks as a single volume.

Apple originally used Core Storage to enable full disk encryption in Lion, but its use has been expanded to Fusion Drive in Mountain Lion. The creation of a Fusion Drive is simple. If you have multiple drives you can create a Fusion Drive yourself using some simple Terminal commands. When you buy a Fusion Drive equipped Mac, Apple does everything for you. Subsequent system and backup restores on your Mac with FD will maintain the Fusion Drive facade, even if you’ve purposefully destroyed the array.

Unlike traditional SSD caching architectures, Fusion Drive isn’t actually a cache. Instead, Fusion Drive will move data between the SSD and HDD (and vice versa) depending on access frequency and free space on the drives. The capacity of a single Fusion Drive is actually the sum of its parts. A 1TB Fusion Drive is actually 1TB + 128GB (or 3TB + 128GB for a 3TB FD).

The latest version of Disk Utility will present a Fusion Drive as a single drive, labeled Macintosh HD from the factory. Apple doesn’t attempt to hide the FD underpinnings however, looking at System Report or using a third party utility like iStat Menus you’ll get statistics on both drives:

If you’ll notice, the 128GB SSD is reported as having a 121.33GB capacity. Since OS X 10.6, Apple has reported capacities in base 10 but if you do the math based on the capacity in bytes you’ll get an idea of how much space is set aside as spare area:

Apple Fusion Drive, SSD Spare Area
  Total NAND Exposed Capacity Spare Area
Apple Fusion Drive 128GB SSD 128 GiB 113 GiB 15 GiB

Approximately 11.7% of the 128GiB of NAND is set aside as spare area, which is no different than what you get with a 128GiB SSD in a standard Mac, but a bit higher than the usual 6.7% spare area you get with most of these drives. The added spare area will help improve performance consistency, but it’s still a bit shy of what I like to see on Samsung SSDs (~25%).

You can create Boot Camp or other additional partitions on a Fusion Drive, however these partitions will reside on the HDD portion exclusively.

Introduction Fusion Drive: Under the Hood
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  • kamsar - Friday, January 18, 2013 - link

    Reliability-wise isn't Fusion Drive basically RAID 0? If it's doing block level migrations and one drive dies there's nothing left.

    Sure hope you've got time machine on... ;)
    Reply
  • pgp - Friday, January 18, 2013 - link

    Yes, technically I think it's more similar to a JBOD configuration, but the reliability should be the same...
    IMHO Fusion Drive is good for noobs, but I'd rather choose which files should be stored in the flash drive and which ones in the mechanical drive, know about the free space in each disk, so I'd prefer a 128GB SSD and, separately, a 1TB hard disk to a 1.1TB Fusion Drive.
    Reply
  • TrackSmart - Friday, January 18, 2013 - link

    I think drive configurations like this are really needed. Maybe not for you and I, but for 99.5% of people. Even people who aren't really "noobs".

    As an example, I purchased a 120GB SSD for a family member who is reasonably good with computers. It breathed new life into a 3 year old computer and was really noticed and appreciated. One year later, the whole thing was a disaster! There are documents, music, videos, etc all over the place. Usually 2 or 3 copies of the same files on both the SSD and the hard drive. Both nearly full. It took several hours to fix the mess.

    Bottom line: Most people can't, aren't willing, or aren't well-organized enough to keep files segregated between drives. Even people who you probably think would be able to handle it by virtue of being reasonably computer literate.
    Reply
  • kmmatney - Friday, January 18, 2013 - link

    I agree. I'm currently all SSD in my work laptop, but going the manual hybrid route in my home computer. Although I'm pretty organized, it is a pain to mov stuff around manually between the drives. For 2 of my kids computers, I just went with Seagate Momentus XT drives, and they've been great. Not as good as SSD, but a fraction of the cost. Reply
  • ToniCipriani - Friday, January 18, 2013 - link

    Multiple copies could be easily avoided, actually.

    On my RAID-0 SSD + 1TB hard drive configuration, I installed Windows 7 in a way that all the profile folders (Users and ProgramData) existed on the hard drive by default, and created NTFS junctions on the SSD to redirect any old software. I never even needed to open the C Drive anymore, and all files and desktop settings reside on the hard drive automatically.

    For older machines XP should support junctions as well.

    Now filling up the drive, that's a different story. And let me guess, the browser got filled up with toolbars too?
    Reply
  • Zink - Friday, January 18, 2013 - link

    Fusion drive is even easier to use than that though and it speeds up all of your programs and files as well as it can with the SSD size given. With a setup like that there are always going to be things on the HDD that get used regularly and they will never see a boost from the SSD. There is the upside of better reliability but outside that boosting 120GB or 240GB of the most accessed files seems even better than permanent segregation. Reply
  • dananski - Saturday, January 19, 2013 - link

    I have manual HD/SSD combinations in my desktop and laptop, have done the same for three PCs I've built for family and have similar setup for nearly every workstation at work. It seems that some users are naturally much better than others at handling their file storage, but I think it's invaluable for people to get good at organising the data systematically and consciously rather than to leave it up to an algorithm that might not have the same priorities.

    I don't like the sounds of every file being written to my SSD then moved to the HDD - I'd get through write cycles for no good reason whenever copying a file to that hybrid drive, and if my HDD doesn't have redundancy I'd feel safer with my important docs on the SSD, even if they're not deemed worthy of the speed boost.
    Reply
  • seapeople - Sunday, January 20, 2013 - link

    Couldn't you just put the "Pictures", "Music", and "Videos" libraries on the hard drive and keep the documents and everything else on the solid state drive? Seems to me like that would work for 99% of people and not require any user thought... So you have a video, you save it in the "Videos" location, etc, and these files would see very little difference being on the HDD vs SSD. Reply
  • Wolfpup - Friday, January 18, 2013 - link

    Yeah, me too. Like my shows from my Tivo are obviously GIGAAAANTIC and don't NEED to have fast access to them. Ditto (even more so) for any music or iTunes stuff. It's not like it's THAT hard to figure out what to put where, but yeah, the average person unfortunately would probably be clueless about it. Reply
  • KitsuneKnight - Friday, January 18, 2013 - link

    It's not so hard if you can get away with just moving your music/videos/images to the HDD. It's much harder if the data you work with is absolutely massive, though.

    One artist I know has a SSD as their boot drive, and 3 HDDs. The PSDs they work with are absolutely massive, and they produce a huge number of them. Working with them on the SSD is far better than the HDDs, but even loading them on that is a bit on the slow side (as opposed to the multi-minute loads from an HDD). But, they have far too many to fit on the SSD.

    So they have the PSDs spread over the 4 drives, filling most of them up, having to manually shuffle them around. Something like Fusion Drive would work far better, as it would be doing exactly what she's doing, just without the manual effort to constantly move old files off the SSD (resulting in multiple hierarchies). The older PSDs would be migrated to the HDDs automatically. And if she starts working on an old set again, they could be promoted back to the SSD... with no user effort.

    And isn't that the point of computers? To make us do less work? It seems a lot of people want to do the jobs of a computer for them. While I'd prefer Fusion Drive to let you pin/hint files to certain drives, I'd say in most cases a 2 drive set up doesn't actually provide real world benefit over an intelligent (which I'm assuming Fusion Drive is) tiering system, even for most power users.
    Reply

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