Digging Into Apple’s Fusion Drive Details

| Dave Hamilton's Blog

One of the more interesting things released today at Apple's event was the new "Fusion Drive" in the new iMac (and yes, it's only for the new iMac and new Mac mini models so far). Fusion Drive is Apple's take on solving the "I want the speed of an SSD but I have way more stuff than I can fit on the SSD I could afford" problem.

Apple Fusion Drive Performance Chart

Apple's Fusion Drive Performance Chart

In a nutshell, Fusion Drive combines TWO drives, a solid state drive (SSD) and a mechanical drive. Apple's initial incarnation puts a 128GB SSD in with either a 1TB or a 3TB mechanical drive. This is not a simple RAID, however, as 100% of the "magic" is done within OS X itself. What Fusion Drive does is it watches what files and applications you run most regularly and it moves them to the SSD. It will also take stuff that you aren't using all that often and moves it to the mechanical drive.

Fusion Drive

Fusion Drive

Not a Cache

To be clear, this is not a caching concept, at least not in the current use of the word. Cache would imply that the data on the SSD is duplicated, and it's not. If you have a 1TB mechanical drive paired with the 128GB SSD, you have a 1.12 TB storage platform. This truly is the fusion of all the space on two separate disks.

Not a RAID

As I said before, this is all being done at the level of the operating system. Disk Utility sees two physical disks, and the OS simply marries them together with Fusion Drive as a layer on top. It does announce just one disk to the user (and to Applications), which means the OS does the management and you don't have to worry about it (but you should still back up).

Fusion Drive Demonstration

Phil Schiller Demonstrates Fusion Drive Concept

What About Backups?

Well, Time Machine will back this up as one volume. If you lose one of your drives (the SSD or the mechanical) you would need to do a full restore, according to Apple. But if you don't have a backup, this setup (unlike a RAID) means you could go in and extract files from the working disk, though I would expect that to be a bit of a chore. Totally do-able, though.

On the subject of replacement drives, Apple did indicate that there's nothing special (or, well different) about the drives in this iMac, so if your 3TB drive failed and you wanted to replace it you could, in theory, do so with 3rd party stuff. You'd have to reconfigure Fusion Drive, and it should work, but of course Apple's not going to support that.

Also Benefits Writes

Since the set up is already there, Apple added a v1.0 iteration (something I love): all write operations are first saved to the SSD. Then, of course, if the OS decides they belong better on the mechanical disk, that data will be moved at another time. But the benefit is that writes happen really fast because they're all going to the SSD.

Sounds Good, Right?

Yes, it does sound good. This may be one of the biggest announcements of the day. 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.

The real benefit, of course, is dependent on how Apple has set up its algorithms to manage all this. But we know how Apple is: it'll be pretty solid out of the gate and then, assuming it's something the company wants to pay attention to, it will get remarkably better over the next 6 to 12 months, too.

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So this is done in the OS.
If I put an SSD in my existing MountainLion Mac in addition to the HD that’s in there could I get the OS to do this?

Dave Hamilton

Unfortunately, no. I asked Apple about this specifically (remember, they had been shipping build-to-order iMacs with both an SSD and a mechanical drive) and they clearly indicated that Fusion Drive is ONLY for the new iMacs.

I’m hoping that changes sooner rather than later.

Stephen Swift

This is a great writeup!  Thanks for the details.  It’s a super cool idea, and something I’ve been wanting for a really long time.  I’ve looked into the hybrid drives before, and just wasn’t really satisfied.  I’m glad to see Apple tackling the problem in their own way.  I can’t wait for it to come to the 21” iMac.  In my dreams, I’d like it to be in the next retina MBP, but there’s no way there’ll ever be enough space.


If it truly is all software, then the only reason it wouldn’t work in a 2011 iMac is if they deliberately check the model name and disallow it.  So, what could be different about the hardware?  They say it’s a stock HDD.  Is the SSD any different?  Or is it the drive controllers on the motherboard that are different? Probably that latter one I’d guess.  Or it could be Apple being a jerk and restricting it to new models on purpose.

John Martellaro

My 2010 iMac has a 256 GB SSD.  Never, never going back to internal HDD of any kind.

Apple probably put considerable investment into this technology, and I can only guess that Phil Schiller’s comment in the keynote applies: some (many?) users just need massive storage AND speed.

I think it sounds sexy at first, but I predict the technology will fade away quickly as SSD prices continue to drop, especially as we explore the nuances of Fusion backups, drive failures.


FYI, the new MacMini can be configured with the fusion drive as well.

John Wenn

According to Apple, the Fusion Drive is available on the high-end 21.5” iMac.


  $1299 low end 21.5” iMac - no Fusion
  $1499 high end 21.5” iMac - Fusion available (only 256GB/1TB)
  all 27” iMac - Fusion available (256GB/1TB or 256GB/3TB). 

Justin Freid

Will it work with older hardware?
In my 13” MacBook Pro I currently have a fast SSD in my optical bay and an upgraded 1TB hard drive in the hard drive bay. I’ve sort of tried to roll my own Fusion Drive by moving things around as necessary.
Any leads on whether the Fusion Drive technology can be applied to configurations without Apple’s blessing? Phil Schiller mentioned that the logic was already built into OS X.

Jerry G

Are you obligated to use the Fusion as a single volume (or partition as a single unit)? Is it possible to separately partition the SSD and hard drive and use each separately as I do in my current iMac, mid 2011, and not have the OS move files automatically between the two?


After I posted the question about using Fusion Drive on older hardware I noticed that the author had already answered it:
“they clearly indicated that Fusion Drive is ONLY for the new iMacs. I’m hoping that changes sooner rather than later.”
Thanks Dave Hamilton


Great write up. Here’s my question: I’m planning on buying a 2012 new iMac. I have a 120gb SSD laying around. Can I order my new iMac without the fusion drive and add it myself later and still get this functionality, or is there some extra piece of hardware in there helping to manage this process in the BTO fusion drive set ups?

I’m sure I’m not the only one wondering, not to mention I’d love to know how difficult it is to do, or for that matter get inside a 2012 iMac. Because the glass is attached to the LCD I’d imagine it will be easier to take apart? If I recall the 2011 iMacs were impossible to upgrade because of all sorts of HD sensor issues. I imagine it will be the same in the 2012 version.


Would work for boot camp, w. windows instaled in a boot camp partition ?  If not, probly slick w. VMware or Parallels.


Apple Fusion Drive—wait, what? How does this work?


Apple did indicate that there’s nothing special (or, well different) about the drives in this iMac

Does this mean these iMacs no longer require the special sensors that previously appeared in iMac hard drives and made replacement very difficult? (As alluded to by Jeff above.)

Jeff also said:

is there some extra piece of hardware in there helping to manage this process in the BTO fusion drive set ups?

I think Dave was trying to say “no” to this when he stressed that there was nothing special about the drives; I think he just means that is there’s no hardware that is dedicated to the Fusion Drive functionality, it’s simply software being smart about how it uses hard drives.


I’d rather to decide what to put in SSD on my own. Some data I don’t use often, but when I use it I’d like it to be fast. vice versa.


“But if you don’t have a backup, this setup (unlike a RAID) means you could go in and extract files from the working disk, though I would expect that to be a bit of a chore. Totally do-able, though.”

Not accurate - you do have the same theoretical option on any RAID-0. Not on RAID-5 of course, but that’s not the comparable RAID level.

Paul Goodwin

Interesting technology. True, SSD pricing is improving, but it’s still at almost 30x an HDD (around $1.40 vs $0.05 per GB). So it’ll likely be years before it’s even close. By then, 10 TB drives will be the market and their prices will continue to decrease. Unless HDD designers reach some density limitation, I don’t see the Fusion drive concept going away soon. And the OS will get more talented about the fusion process. The speed and theoretical reliability advantage of the SSD does make it attractive though, so it’s worth $. Pretty exciting time in computing. It’ll be interesting to see some real-world speed testing results on the new iMac. My mid-2010 is still a great machine though, but it’ll be tough not to drool over these new things. Being behind in technology is psychologically unbearable some days.

Paul Goodwin

Oh…and good article Dave.


Interesting… when I first saw this fusion drive, I thought it was just a hybrid drive like this: http://eshop.macsales.com/item/Seagate/ST750LX003/  But it seems it’s a bit more…


Can I use only SSD (set up my system so it stores everything in SSD) or what happens if I have less then 128Gb data on the drive? Does it go to the SSD only?
I don’t need internal 1TB because I’m gonna use external thunderbolt GTB drive anyway as data storage. What I care is a fast SSD for system only so I would gladly go for a 256GB SSD which was in the previous iMac. The newly announced 768Gb will cost over a €1K which is a ridiculus price and I’m not going to pay it.

Sean Barry

I have been searching high and low but can’t find the speed of the HDD? 5400 or 7200?
SSDs are well under $1.00 a GB now
And I think someone did point out Fusions are available in Mac Minis

RP Navarro

Thanks for article Dave, and comments from all. I’m in, and ordering a top-end Mini Fusion. I’ll report back.

Matt Nadler

Sound like opportunity for a third party solution….

Sumit Kathuria

Can anyone please share the RPM of the 1TB Hard Disk used in the Fusion drive? Is it a 7200 RPM drive or 5400 Drive working along 128GB of Flash memory?


Apple Support’s Fusion Drive FAQ states that “External drives cannot be added to Fusion Drive.”

Does this mean that Fusion Drive can’t be backed up or cloned to an external drive using Time Machine or Carbon Copy Cloner? Seems that would be a major disadvantage. Or am I missing something?


Can I dual boot fusion drive imac with windows 7? If mac OS is what is controlling the file swapping, it will most likely cause conflict if windows is installed. Anyone heard of any confirmation from mac regarding this issue?


“I think it sounds sexy at first, but I predict the technology will fade away quickly as SSD prices continue to drop, especially as we explore the nuances of Fusion backups, drive failures.”

Well, not necessarily. Now a 4TB Fusion Drive is possible, a 5 TB one in a few months. Next year a 10 TB one and in three years a 60 TB one. And so on. That will be much cheaper than a full SSD for the foreseeable future…


I absolutely hate the fusion drive and regret buying it. I got the 27 inch with the 128/3TB combination. Hadn’t done a backup yet when the drive failed. Data is completely irretrievable. In the command line, the computer sees two drives so can’t figure out how to recognize them together to create one image. The data is spread across both, so the best that can get be gotten is incomplete data off each. Neither drive when cloned can be treated as a startup disk or is even mountable.
Apple has no way to fix it. They can only offer the option to wipe both drives and hope that will at least make the brand new computer workable again. It is like a giant, expensive brick taking up space on my desk.
Obviously I am very frustrated about this.
I had the 2008 iMac for 4 years. The only problem I had with is was when the logic board went bad close in the third year. I took it in and it was replaced, all covered by Apple Care.
If I could redo the purchase of the late 2012 iMac, I would have gotten the 256 flash drive and connected a large external drive with Thunderbolt.


Reports indicate Windows cannot see the Mac partition in a Boot Camp arrangement without adding third-party software (HFSExplorer, MacDrive). We all know Windows can see the Mac partition when the drive is a standard HDD or SSD or flash storage (new Air). Anyone know why the Fusion makes the Mac volume invisible to Windows?

Dave Hamilton

@mo666: Yeah, the Fusion drive is a Core Storage construct that OS X had to be specifically built to understand. It is NOT a standard single partition, rather the OS is managing what’s on each physical drive and then internally combining that to present a single UI to the user. Windows doesn’t have Core Storage (or any way of getting it currently, I believe) so, yeah… no Fusion drive access under any OS other than OS X.

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