Mac Technology Explained

What is Apple’s Fusion Drive & How Does It Work?

Tim Brookes 05-09-2013

Solid state drives are awesome 101 Guide To Solid State Drives Solid State Drives (SSDs) have really taken the mid-range to high end computing world by storm. But what are they? Read More . Once you’ve had one, you’ll never want to go back to relying on sluggish hard drive platters and delicate moving parts again. The only snag is that solid state storage is still prohibitively expensive for storing lots of data. While a 256GB or 512GB SSD might be fine for your oft-used apps, OS and local documents; when it comes to terabytes of movies, music and photos Save Space On Your Mac By Storing iPhoto & iTunes Libraries Remotely With my head held low with shame, I publicly admitted last week that I'm a digital hoarder. My once blazingly fast Mac is now left with just 100GB of a 1TB drive left. I've already... Read More an SSD is not a cost effective option.


The days of cheap SSD storage are probably not that far away, but for the moment Apple has come up with an interim solution. By using an SSD and a traditional slow-moving hard drive, the company hopes to strike a balance between space and speed, and the best part is that your Mac will handle all the hard work for you.

Intrigued? Read on to find out how Fusion Drive works.

Fusion What Now?

Fusion Drive is simply the name given technology that uses a solid state drive and a hard disk drive in tandem. The term Fusion Drive doesn’t really mean anything, except when you look at it from a software point of view. Apple’s technology, built into OS X Mountain Lion A Complete Beginner's Guide to macOS: Get Started in Just 1 Hour Our complete guide to macOS will show you everything you need to get started and comfortable with a brand new MacBook or iMac. Read More and later, manages your data using Fusion Drive to best maximise the performance you get out of your Mac.

What is Apple's Fusion Drive & How Does It Work? ssd

This means your Fusion Drive appears as a single volume on the disk rather than showing the SSD and HDD as separate volumes. They are combined into a single logical volume, so you don’t need to think about where you put what. In fact, that’s the best part of it – you simply copy to the hard drive, and OS X handles everything for you.


Whenever data is added to your machine – be it a piece of software, a browser download or your iPhone photos – it is copied to the SSD first. Until this SSD starts to fill up considerably (believed to be around 4GB remaining space), your machine will solely rely on the faster solid state storage. Once you’ve filled up this space, then OS X starts its process of managing your data, but it will always keep a small amount of space free as buffer for incoming data. This ensures file transfers, copies and other incoming disk operations remain as fast as the SSD permits. Because of this, write speeds will always remain fast.

What is Apple's Fusion Drive & How Does It Work? fusiondrive

The operating system monitors your data habits from the word go, even before you need to start using the space on the slower HDD. When the time comes to move data, the OS will do so based on what it has seen you use most often, and that which you use least of all. The movement of this data between drives is not a one-way operation, and the OS will continue to learn based on your habits, and move things around to match your usage.

Partitions, Boot Camp & Price

If you’re considering installing Windows via Boot Camp or otherwise need to partition your Mac’s drive, Apple claims that Disk Utility will allow you to do this to create one additional volume. You cannot partition the SSD, as this is used by OS X solely. Partitioning will create a separate volume which appears as another drive in your Mac, which is not part of your Fusion Drive and thus won’t be used to migrate data. For this reason, this volume will match the speed of a traditional hard drive and forgoes the benefits the hybrid system provides.


What is Apple's Fusion Drive & How Does It Work? imac

In Mountain Lion 10.8.2, Disk Utility would not work with 3TB partitions which meant that Boot Camp Assistant refused to partition a Windows volume. If you’re using a 3TB Fusion Drive, you’ll need to ensure you’re running Mountain Lion 10.8.3 or later in order to do this by updating your Mac using the Updates tab via the Mac App Store.

What is Apple's Fusion Drive & How Does It Work? fusion upgrade

At the time of writing, Fusion Drive must be specified as an extra when ordering your iMac or Mac mini on the Apple website. Unfortunately, Fusion Drive technology is not available in Apple’s line of MacBook computers though if you’re using an older MacBook you can still ditch your optical drive in favour of an SSD How To Swap Out Your Macbook's DVD Drive For An SSD Is your old Apple laptop starting to struggle? Is the boot time so long that you can actually go out and buy a coffee? If so, perhaps it's time to think about upgrading your main... Read More  for speed benefits alone.


For a base-level 21″ iMac or 1TB Mac mini (which already comes with a 1TB SATA hard drive), Fusion Drive adds an additional $250 to the cost. For the base model 27″ iMac, this cost is reduced to an additional $150.

Worth It?

Whether it’s worth it or not depends on whether the additional speed is worth a couple of hundred dollars to you. I’ve been spoiled by my MacBook’s SSD for a whole year now, and I don’t think I could go back to relying on a slow hard disk alone. I also find myself frustrated by a lack of local storage space, and so the idea that a trade-off between space and speed is available for a fee I can stomach seems like an attractive option to me.

I’d say it’s worth it – but would you? Let us know what you think in the comments, below!

Image credits: Samsung SSD (Hong Chang Bum)


Related topics: Hard Drive, Solid State Drive.

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  1. DigitalProductionDan
    November 11, 2013 at 4:01 am

    I actually find it very restrictive. I always partition my drives to insure spare OS partitions that are synced with my main drive in the case of a melt-down. Having a spare os & apps enables you to continue on with your PAID job that a client is waiting for. Clients don't understand "I have to rebuild my 3TB drive" They just want their content finished. When you have a 3 TB drive full of content it can be a real nightmare to manage. I run an OS partition for FCP, a partition to clean my main OS if it become polluted, a partition to TEST new OS versions (1o.9) before I loose a bunch of content due to a glitch in a new release. ALL OF THIS IS NOW OUT-THE-WINDOW! This is not cool at all. We should be given the option of customization if we want it. My iMac only came with 128GB of flash for fusion. It doesn't do anything as it is way too small. Now I have to buy a 256 or 512. Not fun. If anyone finds a way to give me back my control please shoot me an email.

  2. Anonymous
    September 6, 2013 at 1:49 am

    Been on PC for a long time

  3. dragonmouth
    September 5, 2013 at 11:41 pm

    The only problem with SSDs is that allow for a limited number of writes, or at least much more limited than HDs.

    • Tim B
      September 6, 2013 at 1:42 am

      They do, but this number is so high that for most people (read: common users) it makes absolutely no difference to the life of the machine. They will end up replacing their computers before the NAND reaches maximum number of writes.

      Compare this to mechanical HDDs which are far more susceptible to sudden death thanks to spinning parts, a moving arm and very delicate platters. I'd always recommend users buy an SSD or an SSD hybrid drive over a standard HDD these days, partly because I've been spoiled by the speed of my own SSD. It makes everything _so much_ faster!

  4. Joshua
    September 5, 2013 at 9:18 pm

    Idea pirated by Intel. Dude, Apple gets lazy with it's own inventions...

  5. max ravazzolo
    September 5, 2013 at 5:42 pm

    I have actually made a Fusion Drive on my 2010 Mac Book Pro, installing a 256mb SSD on the disk bay and keeping the existing 320 gb hard drive. The operation is not officially supported, but I found the instructions on line and it worked perfectly. I've been running it for an year now, and I'm amazed at how good it is, the speed increase feels like two-fold... So I have a three years-plus old laptop that is still satisfying in all aspects. Amazing!...

    • Tim B
      September 6, 2013 at 1:45 am

      That is really cool! Where did you find the instructions? I'd be interested in looking them over. Did you just set it up as a Fusion Drive in Disk Utility?

      And yes the speed is exhilarating, especially compared to the platters of old!

    • Max
      September 6, 2013 at 10:54 am

      It's a low level formatting, which can only be done by starting up with a USB startup drive and using the Terminal version of Disk Drive to "conglobate" the HD with the SSD. I can't remember exactly where I found the instructions, but if you google it I'm sure you'll find it.

      Btw, I installed the SSD at the place of the DVD drive, OWC sells a great kit for that...

    • Donal
      November 22, 2013 at 7:49 am

      Creating your own fusion drive is a command line process.
      See the following link for full details.

      But it is only two commands. I have done it for a 2011 MBP (with replacing the DVD with SSD) and a MacMini Server (replacing one of the HDs with an SSD). Both times the operation was simple and worked 100%. Afterwards you really see a massive speed bump. Not to mention the nice increase in capacity. Especially in the day to day things of opening files and starting/stopping virtual machines you really get the full impact of the SSD. I would say that it alone has extended the life span of the machines by an additional 3 years. If however you decide to copy in a 50GB music or photo library or rip and convert movies (CPU intensive) then you are back to the old speeds. But these are not normal day-to-day tasks.
      By far the most difficult task in creating a fusion drive is opening up the machines and replacing the hardware. But there are macsales videos to help. To create the fusion drive the machine must be booted up from an external drive and creating this is also a task to be learnt. But it is a useful skill and may save your bacon some day if you have a system failure.

  6. Dominic
    September 5, 2013 at 5:34 pm

    ...Or you can buy a Segate Hybrid drive for half the price and have it benefit Windows too...

    • Theron
      September 5, 2013 at 8:40 pm

      This is true but the SSD portion is usually only 32 gigs or only slightly larger.

    • Tim B
      September 6, 2013 at 1:51 am

      Apparently the NAND included on the latest third generation drives is only 8GB, according to Notebook Review anyway. While any NAND storage provides noticeable benefits, it's quite a way away from the 128GB SSD included with Apple's technology. Apparently, due to this, much of the benefits disappear during data hungry operations and much of your data would still be stored on a HDD rather than the SSD because of the space requirements alone.

      Also aren't the Seagate Hybrids all-in-on SSHD design? As stated in the article, Fusion Drive uses two separate drives, an SSD and a HDD, which is married via software. I'd have thought similar technology exists for Windows, though I'm not sure (I haven't checked) whether Windows 7/8 handles separate volumes in a similarly efficient way to OS X. I hope it does/will do in the future though.

    • Dominic
      September 6, 2013 at 9:17 pm

      Mac has you all fooled by calling it cool names. It's a SSD / HDD hybrid.
      All Hybrid drives use two "separate" drives. Apple has just marketed it in a way that fool you.
      Wake up people this is classic marketing trickery. Apple has made no advances except calling it "Fusion" and stressing standard features of existing hardware to make it seem "revolutionary"
      You can do the same in windows with an SSD and Hard drive separately on Windows. It's called READYBOOST and it works with USB storage too.
      Linux has built in options too, but it is more manual.

      This is nothing new, innovative or revolutionary. It is Apple trying to market already available technology aggressively enough that people will again believe that it is a product of Apple (Just like INTEL'S Thunderbolt IO port)

      Fanboys will be fanboys.

      Fusion drive is a cheap hybrid drive splashed with an apple logo and priced at 3x its value.

    • Tim B
      September 6, 2013 at 11:55 pm

      I'm afraid that's not quite right. The latest hybrid drives are standard hard drives with a couple of cells of NAND incorporated in the unit. That's an SSHD. You install it as one drive, it appears as one drive ergo – it's one drive. As opposed to using a full-sized SSD (in this case 128GB, rather than the rather meagre 8GB) and a standard HDD, up to 3TB. That's an SSD and a HDD, used in unison, and managed by the OS. I never said it was brand new Apple technology, because that's not what this article is about.

      As far as I'm aware, ReadyBoost is only handling the caching side of things and does not intelligently move your files around based on usage. I've since looked this up and what little information I can find confirms it. As I said in the article, Fusion Drive doesn't really mean anything until you look at it from a software point of view, at which point it means more than an increased cache or a slither of NAND to boost write times. It's two storage mediums joined together by software in a way that users don't even notice it's there, but reap all the benefits of using solid state storage.

      Your use of quotation marks implies that I said it was revolutionary (I did not), nor did I say Apple invented the technology. I didn't bother, because the article is aimed at people who want to know what the marketing jargon means, rather than Windows users hung-up on slagging off Apple all the time.

      But do tell me more about what a terrible company Apple is for making use of perfectly serviceable technology and marketing it in a way that makes their potential customers actually want to buy it.