Fusion Drive on the Mac: Combine SSD and HDD hard drives into one volume

Apple Fusion Drive - HDD and SSD hard drive combined

The "Fusion Drive” from Apple is an option that has been available for Macs in the Apple shop since October 2013. Technically, it is a combination of an HDD hard drive (the models with rotating magnetic disks) and SSD (hard drives that work with flash memory). The operating system combines both hard disks into one volume, so that instead of two separate disks, you only see one large hard disk in the Finder.

Apple Fusion Drive - HDD and SSD hard drive combined
Apple Fusion Drive - HDD and SSD hard drive effectively combined. The article explains the advantages and disadvantages of this and how you can set up a Fusion Drive on the iMac at a later date.

Benefits of the Apple Fusion Drive

The advantages of the Fusion Drive are as follows:

  • a large, slow (HDD) and a none, fast (SSD) hard drive are combined into a fast one
  • the storage space of both hard disks is bundled together into one
  • The OS X / macOS operating system automatically stores files that are often used on the fast SSD, which makes the Mac much faster
  • The Fusion Drive is usually cheaper than a similarly sized SSD, as this type of hard drive is still quite expensive

Cons of the Fusion Drive

In addition to the advantages, there are also some disadvantages that you should keep in mind when combining your HDD hard drive with an SSD to form a volume:

  • a Fusion Drive has one higher risk of data loss, because only ONE of the two hard drives has to break and the entire volume is no longer readable (for this reason, a backup is strongly recommended!)
  • a pure SSD always has advantages in terms of speed, because ALL data can then be read and written quickly
  • Because there is always an HDD involved in the Fusion Drive, the “common” hard drive will never be as silent as a pure SSD

How much performance does the Fusion Drive bring in comparison to the HDD hard disk and the SSD

On the English-language Anandtech blog I was able to find a post in which someone used a Fusion Drive in comparison to the HDD and a pure SSD in his everyday life. The results of the various tests are hardly surprising: the pure SSD is always the fastest solution, the pure HDD (hard drive with rotating disks) the slowest and the Fusion Drive moves somewhere in the middle.

Fusion Drive compared with HDD and SSD hard drive - Photoshop CS6 Start
Fusion Drive in comparison with HDD and pure SSD hard drive - here the start of Photoshop CS6: shorter bars are better (source: Anandtech).

Do you prefer Fusion Drive or pure SSD?

If you really want maximum performance and are ready to make some money for it, you should buy a pure SSD. Here, too, you can connect an external SSD to the Mac (via Thunderbolt or USB 3.0) and then copy the entire system with all the data to it (the Super Duper or Carbon Copy Cloner help here). Then you can also boot from the external SSD and use the internal drive as a Time Machine backup volume, for example. So you always have the solution with the best performance.

Upgrade MacMini or iMac with external SSD to Fusion Drive

If you still have an old Mac with a slow hard drive installed, you still have a few options to get it faster. On the one hand, you can (or have it replaced) by yourself (or at an Apple dealer) for an SSD hard drive. Alternatively, you can pack an external SSD in a Thunderbolt housing and then create a Fusion Drive with the internal HDD hard drive. Of course, this is only possible if your Mac already has a Thunderbolt connection.

If this is available, then you can, for example this Delock Thunderbolt housing (Don't forget the Thunderbolt cable!) And one 128 GB Samsung SSD build an external SSD, which then becomes part of the Fusion Drive. The 128 GB are usually easily enough, as the operating system usually only swaps out a large number of small files on this disk. The SSDs that Apple itself installs in the Fusion Drives are usually many times smaller.

Finally, all you have to do is combine the two hard drives into a Fusion Drive volume. I will write instructions for this in the next few days.



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8 Responses to “Fusion Drive on Mac: combine SSD and HDD hard drives into one volume”

    1. Hello!
      Thanks for the comment. Unfortunately, the creation of the instructions has been forgotten a bit and only slipped back into the foreground with your message ...
      But I immediately sat down and hope that these instructions are as user-friendly as possible: just click here
      Good luck with the merger!

  1. Quote:
    A Fusion Drive has a higher risk of data loss, because only ONE of the two hard drives has to break and the entire volume is no longer readable (for this reason a backup is strongly recommended!)
    —————————————————————————————————————————————————— ————————-

    Isn't that quite right ??? An SSD can also break and what about the data? So, of course, you have to make backups of an SSD too. Data that are not used often do not have to be read so quickly otherwise they would not be transferred to the HDD. The advantage is clearly with a FusionDrive - it is fast and cheap, the system lies on the SSD part and is faster in the long term (because data is swapped out) than a pure SSD drive on which all data is also stored.

    1. Hello Jeckyl! I think you misunderstood the statement. Of course, SSDs also break. In fact, they tend to be more likely to fail because they are not designed to be overwritten frequently. The mechanical hard drives can withstand more write cycles. But what it was actually about: If you have distributed your data on two hard disks (regardless of whether it is mechanical or SSD), the mathematical increase in the chance of data loss due to a hard disk crash increases. Simply because only one of the two disks has to fail for all of the data to be lost.

      But you are also right that the Fusion Drive is the best alternative in terms of price-performance ratio. You have a good price and still fast access times. And basically you should have a backup for all hard drives ... no SSD or HDD is 100% secure.

  2. Hallo,
    I would like to dissolve my Fusion Drive that was already built into the iMac and have an SSD installed instead of the HD. After that I have the 128mb from Apple and a new Samsung 1gb.
    I wanted to use the Samsung for the OS.
    What is the best way to proceed? Is it even feasible?

    1. Hello East! I think you still need an external hard drive to which you can first clone the Fusion Drive (with Carbon Copy Cloner or Super Duper for example). Now you install the new internal hard drive. Then you boot from the external hard drive and format the two internal drives (128 GB and Samsung 1 GB) with the hard drive utility. I would then use the Samsung disk as the new main disk. Creating a Fusion Drive from two SSDs would be counterproductive, I think. You can use the small Apple SSD for storing important documents as a backup or something. Or as an emergency partition ... I hope this helps you with the implementation!

  3. I've been using an iMac with Fusion Drive for years and now the problem is that the small 250 GB SSD is almost full, the large 2 TB HD still has a lot of space. I have never dealt with storage on these two plates and am faced with the question of how and what I can move from one plate to the other.

    1. Hello Dirk!

      In any case, you can outsource the iTunes media library and, if necessary, the photo library. This means that two big "Kloppers" should be gone. Otherwise, I can still recommend that you clean your Mac every now and then with the “Clean My Mac” program. This makes sense especially for people with an SSD, since you can quickly free up 15 GB and more here. I have here is an experience report wrote about the program and I still use it every 1-2 weeks today. How to outsource the iMovie library, I have here explained. It works exactly the same with iTunes and the photo library ... same principle, only different folders. LG! Jens

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