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 - Friday, January 18, 2013 - link

    I purchased a mid range mini a Qaud 2.3 with just a 1tb hdd. I added a samsung 830 512gb ssd as the second drive. If you put the ssd in with no format and boot with an external drive you then go to disk utility the internal ssd and internal hdd are highlighted in red. The disk utility sees it as a broken fusion answer yes to fix it and in under a minute you have a 1.5tb fusion. then do an internet recovery to load mountain lion and you have a standalone mac mini with a killer 1.5tb fusion. Everything you mention in your tests(about the ssd being taxed) is less true basically because the ssd is huge and in a 1 to 2 ratio with the hdd. This is the closest I have come to a 1.5 tb ssd.

    I copied a 500gb eyetv folder with 30 18gb recordings easy peasy. So if you have a 2012 or even a 2011 mac mini and mountain lion just add a big ssd and fusion away.
    Reply
  • hypopraxia - Friday, January 18, 2013 - link

    I am with you on this one. Fusion drive with a higher SSD to HDD ratio nets huge gains in snappiness and overall SSD-ness of the fusion drive. I have only encountered IO slowdown once or maybe twice in the 2 months I've been running with Fusion. Reply
  • MaxComrie - Friday, January 18, 2013 - link

    Love my job, since I've been bringing in $5600… I sit at home, music playing while I work in front of my new iMac that I got now that I'm making it online(Click on menu Home)
    http://goo.gl/xeJPd
    Reply
  • Samus - Saturday, January 19, 2013 - link

    ^^ SPAM ^^ Reply
  • Munkyman42 - Tuesday, March 05, 2013 - link

    eeep!

    I wonder if this'll work on my 2010 Mac Mini Server. If I can squeeze another year or two or performance with even a 64GB SSD upgrade my wallet would be thrilled!
    Reply
  • Mr_SkoT_A - Tuesday, May 14, 2013 - link

    I have done it on a late 2008 Unibody Macbook and an original Mini Server. Works like a charm! Reply
  • Hughmungalous - Friday, August 30, 2013 - link

    I DID IT on a late 2008 macbbok ;-P 250GB Samsung 840 with a WD Blue 640GB HDD its been in a fusion for about 3 months now and runs beautifully... its basically a media server for me and my wife and it never slacks on its duties!!! its snappy switching profiles and logging in and out... wifey uses safari and flash games and what not and i never hear her complain anymore about her slack windows computer... i use it for heavy downloading light gaming and media server. Mr_SkoT_A Just installed i did the fusion setup which was fairly easy, except i used a specific number and got a 860GB drive instead of using a "100%" value to create the (correct amount) 890GB drive so i have 30GB of my drive in fusion limbo right now... all in all i love it the samsung drive was a smart buy i would love to hear from someone who runs with like a 60gb SSD and a 1TB HDD would be nice to know how much money i could have saved Reply
  • techdaddy1 - Wednesday, May 29, 2013 - link

    Hello...can you please clarify regarding booking from an external drive? So you're saying you just installed a ssd you purchased into the machine in addition to the HDD that it came with and disk utility automatically created the fusion? did you need any extra parts to install the ssd? Anything you could tell me would be appreciated. I just purchased the Quad 2.3 Mini as well. Thank you for your time :-) Reply
  • niccopernicus - Sunday, November 03, 2013 - link

    I just had my original iMac (recent (not the newest) model with a 2.93 GHz Core i7, now running Mavericks) hard drive replaced with a larger one. I had a 512 SSD installed at the same time, which was formatted and ready to use when i got it back. Is there a way to do the manuver you describe above with Disk Utility now that has already been formatted? Reply
  • hypopraxia - Friday, January 18, 2013 - link

    So, after I read up on core storage, I rolled a fusion drive in my 2011 macbook pro 13", using a 240GB SSD (sand force controller) and the stock 320GB HDD. (I removed the optical drive. Stupid optical drive...) It honestly feels like a 550GB SSD. Then again, My ratio of SSD to HDD is 3:4, so as always, YMMV. Reply

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