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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  • philipma1957 - Sunday, January 20, 2013 - link

    I have a 2012 quad 2.3 mini using a 512gb ssd and the oem 1tb hdd. It works very well. I used to run this mini with 2x 512gb ssds in raid0. They were in a pegasus r6 case hooked up via t-bolt. I now run this with the 1.5 tb fusion and a tm plus a clone backup in the thunderbolt case. I prefer the setup this way. I have been doing this for a week I have about 480gb on the 1.5tb fusion . It will take me a while but I will put about 1tb on the fusion I will then see how much it slows. Reply
  • pichemanu - Saturday, January 19, 2013 - link

    A chart illustrating the possible impact of a USB 3 bottleneck on your test:

    http://tinypic.com/r/34fir7m/6

    Suddenly the fusion drive no longer looks that good ;).
    Reply
  • mrbreaker101 - Saturday, January 19, 2013 - link

    I have a 2011 Macbook Pro with a 128GB Corsair Force 3 SSD and a 500GB hard disk. I decided to run the commands to make a fusion drive and so far, it's working, although the Force 3 isn't running that fast, despite being set to 6Gbps SATA.

    I'm going to install some new hardware in my iMac next. A 256GB Kingston Hyper X 3K SSD and 2TB hard disk (with thermal sensing cable from OWC, essential for iMac custom hard disk installs).

    I'm not entirely sure I want to make a Fusion drive on the iMac as well. My current usage is about 500GB, with most of that being music files. On one hand, I have no need for mp3s using up my precious SSD space, even if I listen to them 1000 times a day. On the other, the simplicity of no longer having to worry about the locations of files is very appealing.

    I also wonder, if I do a fresh install of Mountain Lion and then re-import my photos, media, etc, will Fusion Drive work better than by migrating over a Time Machine backup, which may fill the SSD with music, but leave apps on the hard disk?
    Reply
  • ThomasA - Sunday, January 20, 2013 - link

    I have no experience with the 'fusion drive' but wonder about a clone/backup method, given the circumstances.

    I do have a MBPro with a 256GB SSD paired with a 'spinning' HD (replacing the DVD).

    I followed instructions offered by a Matt Gemmell, re: moving the 'home folder' to the HD. This allowed a backup clone of the SSD & a separate copy of the HD files.

    http://mattgemmell.com/2011/06/21/using-os-x-with-...
    Reply
  • twotwotwo - Sunday, January 20, 2013 - link

    Awesome that Anand can't resist throwing in some sort of enterprise-y benchmarks in a review of a consumer thing. :)

    I'm sort of curious how the enterprise caching solutions work on the real-world database-y workloads I've seen AnandTech do measurements of before. That's super workload- and software-dependent (how big is your working set? how fat is your long tail of requests outside it?) so AT's results wouldn't directly apply to the world at large--still, one data point is a big step ahead of zero. :)

    (It also seems to be increasingly a thing to design enterprise stuff with data 'intelligently' routed by to SSD or HDD by application-aware software [Evernote has done this, say, and Amazon offers SSDs and HDDs in separate instance types], rather than routing with magic at the block device layer. Still, would be awesome to know anything at all about how effective the automagical caching is in databases.)

    And, unrelatedly, I'm sure Apple will get rid of the Pros with HDDs when they can, and I hope most other manufacturers do, too. You don't need TBs of internal storage now (esp. if videos are streamed, cloud storage an cheap externals exist, etc.) and Flash is good for speed, size and weight, durability (no head crashes!), etc.
    Reply
  • carraj - Saturday, January 26, 2013 - link

    Machine: 2010 15" MacBook Pro, 8 GB RAM. Disk controller is SATA II, so pointless using SATA III devices.

    Installed 750 GB WD Scorpio Black HDD in optical drive bay using Data Doubler bracket (/dev/disk1).

    Installed 240 GB OCZ Vertex Plus R2 SSD in HDD bay (/dev/disk0).

    Both were formatted as JHFS+ using Disk Utility. A Recovery HD partition was created on the HDD using Carbon Copy Cloner as /dev/diak1s3.

    Fused /dev/disk0s2 and /dev/disk1s2 together giving ~1 TB Fusion Drive.

    Performance is incredible, though not quite as fast as my mid-2012 13" MacBook Air with 256 GB SATA III SSD in tests. Here are the results from Xbench 1.3 (the Fusion Drive clocks in at about 2/3 of the performance of the pure SSD, despite having a 3 Gb/s SATA II interface rather than a 6 Gb/s SATA III interface):

    15" MBP with 240/750 GB SATA II Fusion Drive:

    Disk Test 277.85
    Sequential 180.25
    Uncached Write 412.52 253.28 MB/sec [4K blocks]
    Uncached Write 278.11 157.36 MB/sec [256K blocks]
    Uncached Read 89.26 26.12 MB/sec [4K blocks]
    Uncached Read 201.26 101.15 MB/sec [256K blocks]
    Random 606.00
    Uncached Write 555.66 58.82 MB/sec [4K blocks]
    Uncached Write 531.52 170.16 MB/sec [256K blocks]
    Uncached Read 1566.27 11.10 MB/sec [4K blocks]
    Uncached Read 438.38 81.34 MB/sec [256K blocks]

    13" MBA with 256 GB SATA III SSD:

    Disk Test 431.86
    Sequential 278.39
    Uncached Write 720.45 442.35 MB/sec [4K blocks]
    Uncached Write 479.45 271.27 MB/sec [256K blocks]
    Uncached Read 106.55 31.18 MB/sec [4K blocks]
    Uncached Read 662.54 332.99 MB/sec [256K blocks]
    Random 962.48
    Uncached Write 751.67 79.57 MB/sec [4K blocks]
    Uncached Write 748.11 239.50 MB/sec [256K blocks]
    Uncached Read 2147.57 15.22 MB/sec [4K blocks]
    Uncached Read 977.31 181.35 MB/sec [256K blocks]
    Reply
  • kamaaina - Tuesday, February 12, 2013 - link

    I am very happy after 6 weeks with my DIY Fusion Drive in my MBP. Replaced the optical drive as well and moved the HDD 500GB Momentus XT into the DVD HDD tray, and put an Intel330 240GB SSD in. Fused together, it runs really well. I followed the video on Youtube from Tomas Villegas, took me a only a few minutes. Awesome improvement! Reply
  • qzyxya - Saturday, February 16, 2013 - link

    Is there a way to get this for windows? I'd love to have this. Like buy a 128gb ssd and use it for caching with my 3tb samsung 7200.14 hard drive Reply
  • navss - Friday, April 26, 2013 - link

    Great read, personally I like the thought of getting the Mini with the 256GB SSD + adding another 2-3TB HDD for relatively cheap and using that terminal command to set up the Fusion Drive.

    Also Anand, if you're going to be taking screenshots of programs on the Mac: Cmd+Shift+4+(hover over the program you want a screenshot of) then hit the spacebar, you'll get much nicer screenshots.
    Reply
  • Mortenling - Wednesday, May 15, 2013 - link

    When (not if) the fusion drive breaks down it is almost impossible to replace it in the new iMac's. But will the SSD part of the fusion drive still work if its only the normal HD part there is broken ?
    I'm not sure if i should go for the fusion drive or the 256 SSD in a new iMac. I need to fill it up with music applications and i'm not sure if there is space enough in the 256 SSD but I'm sure it will last longer. I don't think you can create a fusion drive with an external HD but is it possible to create some sort of RAID with an external SSD to give me a total 512 SSD HD. At the moment I cant afford the internal 512 SSD but that I think would be the best solution. I need some advice so please help me out here :-)
    Reply

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