How to create a Fusion Drive on older iMacs

Last Updated: Sep 23, 2020

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Apple announced a new storage technology, called Fusion drive at an Apple Media event last October. Fusion Drive, which is available as an upgrade option in Built-to-order (BTO) iMacs and Mac Minis combines Solid State Disks with regular spinning disks, thus offering high performance and high storage capacity at the same time.

Apple describes Fusion Drive as:

Available as a configurable option at the Apple Online Store, Fusion Drive is a breakthrough concept that combines the high storage capacity of a traditional hard drive with the high performance of flash storage. With Fusion Drive in your iMac, disk-intensive tasks — from booting up to launching apps to importing photos — are faster and more efficient. That’s because frequently used items are kept at the ready on speedy flash storage, while infrequently accessed items go to the hard drive. The file transfers take place in the background, so you won’t even notice. As the system learns how you work, Fusion Drive makes your Mac experience even better. And you don’t have to do a thing.

I own a late 2009 27″ iMac that I upgraded to 16GB of memory and 2TB hard disk space. A couple of months ago I switched to a 512GB Crucial M4 Solid State Drive, but I quickly realized that 512GB are pretty tight. Then in October Apple announced Fusion Drive and made it available to newer iMacs and Mac Minis. Shortly after, I read that Patrick Stein aka @jollyjinx figured out that OS X 10.8.X supports Fusion Drive on older Macs as well, as long as you have both a spinning and a Solid State Drive connected via SATA.

So I decided to give Fusion Drive a spin by opening up my iMac and installing both the spinning disk as well as the Solid State Disk I already had.

Parts and tools

Before taking my iMac apart, I downloaded OS X Mountain Lion from the App Store on my MacBook Pro and copied it to a bootable USB stick using a utility called Lion Disk Maker. Despite the name, it also works with Mountain Lion.

To take out the motherboard of my iMac, I pretty much followed a guide by Brian Tobey – the only difference between his iMac and mine I discovered was that mine did not have a spare SATA connector, so I had to disconnect the optical drive (which I barely used anyway) to plug in the SSD SATA cable. Also, my motherboard layout was slightly different, but that was not a big deal. To make sure I could re-assemble the iMac, I took a picture of my motherboard before unplugging all connectors. I also mounted the SSD right under the optical drive and put everything back together. To my surprise, the iMac booted up right away – a sign that I correctly wired at least the major connectors :)

Next, I booted off the USB thumb drive by pressing the Options key during boot up and then selecting the thumb drive. That loads the Mountain Lion recovery environment. Once the recovery environment was up and running, I opened Disk Utility to confirm that OS X saw two hard drives, my 2TB Seagate Barracuda and my 512GB Crucial M4. Then I opened up a command shell to create a logical volume spanning both disks. I followed pretty much the guide of Patrick Stein with some minor exceptions.

On the command line I first issued the following command to figure out what disks I was dealing with:

diskutil cs list

In my case, disk0 was my SSD and disk1 my spinning disk. Then I issued the following command to create a logical volume spanning both disks – “blah” is just a dummy name and you can certainly choose another label:

diskutil cs create bla disk0 disk1

Then I ran another

diskutil cs list

And marked/copied the ID of the Logical Volume Group. It has the following format (but your ID will be different of course): DE85044F-EADA-4F26-93B7-8CD0ADF006EC

Next, I created an HFS+ volume using the following command (replace the volume ID marked in bold with the one on your system):

diskutil coreStorage createVolume DE85044F-EADA-4F26-93B7-8CD0ADF006EC jhfs+ blub 2500g

The label “blub” you can certainly change to whatever you want to and the 2500g (meaning 2500 GB = 2.5 TB) can be changed as well to match the combined size of your two disks. In my case I had a 2000GB spinning disk and a 512GB SSD – so I used 2500g in the command above.

If all the commands above executed without errors, you now have a 2,500 GB Fusion Drive. Last but not least, quit the Terminal and start the installer, which should now see only one available disk to install OS X on.


  • Since I replaced the original Apple 1TB spinning hard drive with a non-Apple Seagate Barracuda, the temperature sensor connected to the drive could no longer sense the temperature correctly. This is a known issue caused by Apple using a different PIN configuration in its sensor cables. There are two workarounds for that – you either shorten out the sensor cable with a paperclip, or you buy a third party application that monitors the HDD temperature through SMART and controls the HDD fan accordingly. I opted for the latter by purchasing a copy of HDD Fan Control.
  • I haven’t had time yet to perform IO tests, like the ones Patrick Stein has done but based on what I’ve seen so far, my IO performance is much better than it used to be with only the spinning disk.
  • Taking out the motherboard of your iMac and installing an SSD may or may not void your warranty – I just don’t know. The fact is, that none of what you’re doing if you don’t damage anything, can’t be undone. So worst case, you put everything back to how it was before taking the iMac to the Apple Store (if it needs repair).

Thanks to Patrick Stein and Brian Tobey for their articles! Let me know if you have any questions or issues.

27 thoughts on “How to create a Fusion Drive on older iMacs”

  1. Hi Michael:

    Thanks for these instructions. I have a mid-2007 iMac (imac7,1) and wonder if I could do this with my iMac. Thanks.

  2. Hi,

    You don’t need to download the installer from the App Store and burn the USB/DVD. This can all be performed from the Internet recovery service by holding cmd-alt-r on startup (or the drive selection window).

    Just did it on my April 2010 MacBook Pro.

    Thanks for the rest of the instructions- I think the initial diskutil cs list line should just be diskutil list though.

    • Hi Lucas,

      You are right, any means to boot into the recovery console/installer works, including Internet recovery.

      As far as the command line is concerned I do believe you want to list coreStorage but it could be both output the IDs we need, I never tested yours.

    • Hi Ace,

      you may not have disk0 but disk1, disk2 or diskX. Just read the following part of my post again and pay close attention to the output of diskutil cs list !
      Replace the disk numbers with whatever you see in the output of above command!

      On the command line I first issued the following command to figure out what disks I was dealing with:

      diskutil cs list
      In my case disk0 was my SSD and disk1 my spinning disk. Then I issued the following command to create a logical volume spanning both disks – “bla” is just a dummy name and you can certainly choose another label:

  3. OWC is reporting that this process does not actually yield a “real” Fusion drive unless run from Mac Mini lat 2012 diskutil. Instead, you get a drive that does not intelligently reallocated data. This seems to be at odds with what some others have reported, but OWC generally knows what they’re about:

    Can you confirm that this is actually intelligently reallocating space between drives?

    • I just read their article…I think they are wrong. Diskutil should be the same no matter what HW. Just make sure you download a fresh copy of OS X from the App Store (to create the bootable USB stick), which should come with the very latest version.
      I had no issues doing that on my 2007 iMac.

      • Disk Utility do have different build numbers on different macs, evwn with the same version number (13). The build number on my Mac Pro is only 430 with 10.8.2, while the 2012 Mac mini has build number 444. So while this allows for a single logical unit, it does not do the automated tier based allocation of files that the fusion drives do.

        • Ragu,

          Disk utility has got nothing to do with how the OS handles file system calls. All you need Disk Utility for is to setup the volume – after that it is out of the picture and FS drivers take over. What evidence have you seen that makes you believe the disk utility build number plays a role in this process?


          • Mostly from the OWC blog as their tech people seem to portray this – I could see this as likely, but you are right, I don’t have solid proof. However, I’d like to see some data that this is really a Fusion drive and not a “dumb JBOD” drive, i.e. how do you know that there is 4GB always being held as empty on the SSD where automatic tiering of your data takes place? Without this, basically you’ll always see a performance increase initially cause you haven’t even filled up your SSD with data, but as soon as you do, you’ll just get normal hard drive speeds since that is all you are doing. Even if you aren’t touching the files on the SSD, they aren’t ever going to be moved to the normal hard drive (unless you have proof that this system is actually occurring with your method).

            Fusion Drive = JBOD (SSD + HDD) and Automatic Tiering.

            You’ve definitely shown how to make the JBOD, but I don’t see any evidence of the automatic tiering.

  4. Hello Michael,

    thank you for your detailed instructions. I am just confused about one part.

    Just today I bought a used iMac which came installed with a 256 GB SSD and a 2 TB HDD.
    Mountain Lion seems to be installed on the SSD. The 2 TB HDD is a separate volume and is empty.
    Do I need to make a bootable USB stick for this to work or can I just punch in the command lines into terminal? Thank you for your help.

    • You still need to make a bootable USB stick and re-partition/re-format the drives as per my instructions. So make sure you have a backup of your data that you can restore afterwards since the re-partitioning will wipe out all data on both drives!
      Hope that helps!

      • Thank you for the clarification.
        The problem I encounter now is that Lion DiskMaker could not find my installer, and I can’t just re-download mountain lion in the app store, because I haven’t bought it with my Apple ID (the previous owner probably purchased it with his Apple ID). I also tried the other solution suggested in the Lion DiskMaker help file but that didn’t work either.
        Do you have any suggestion on how to solve my problem, I looked hard into it but I just can’t figure it out.

        • The installer won’t be there unless you explicitly download it through the AppStore. Once downloaded quite the installer and run the Lion DiskMaker. Without the download you have to get the installer from somewhere else. Just having Mountain Lion installed is not sufficient.

          But if you cannot purchase Mountain Lion in the App Store because it is marked as purchased already (by another Apple ID) you’d have to contact Apple and ask them how to “reset” that. Alternatively you could boot into the Apple recovery environment (COMMAND + R) at reboot and re-install OS X (without wiping the complete drive and thus the recovery partition). Then purchase/download Mountain Lion and re-partition the disk.

          Hope that helps!

          • After some more reading and playing around I was finally able to finish the process of creating the fusion drive. One thing I had to change from your instructions was changing the first command from “diskutil cs list” to “diskutil list”. Everything else worked perfectly. Thank you again for your help.

  5. Can someone give a easy instructions for a noob like me to put the code where and how ? I have already installed the extra ssd drive successfully. I just need to make it fushion.

    • Hi Mrk! After you have put in the extra SSD you need to boot into the OS X recovery console/installer. I did so by booting off a USB stick that I had loaded the installer on (using the Lion Disk Maker). Once in the recovery console you can open a console and punch in the commands I mentioned in my article.

      If that doesn’t help, can you please let me exactly at what point you’re stuck or what’s unclear?


  6. Hi Michael,

    Thank you for your reply. After reading your instructions a few more times to gain the full understanding what I was getting into, I went ahead a created a Fusion disk. The concept is similar to manually creating a striped raid system without losing disk space because of differences in disk size. I am using my new Fusion disk now. Performance wise, it is take me a few days to see if there is any. Thanks again for your response and instructions.

  7. It seems that when you get a Fusion disk, your current volume(s) content (apps/files) remain the unharmed. Is this correct? Thanks.

    • That depends on what you mean by “get a Fusion Disk”. If you upgrade your old iMac to a Fusion Drive, like I described in the article, then you’ll have to wipe your drive completely (and then restore a backup for example).

      You cannot convert a regular drive into a Fusion disk (by adding a 2nd drive) without reformatting the volume.

  8. Hi Gavin,

    correct, you’ll get the same Fusion Drive experience as you’d get on newer iMacs. Theoretically it should work on MacBook Pro’s as well but I haven’t tested it.

  9. That’s sounds amazing. With this system, does the OS learn what you use more frequently and move it to the SSD side and visa versa like Apple states? In theory you can have the same fusion drive as the new iMac’s on older ones then?
    Do you know if this is also possible on a 2010 MacBook Pro 17″ if you replace the optical drive with the SSD?


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