I have a Mac Min Late 2014 with a 1 TB fusion drive

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I want to replace it with something like this OWC 2TB SSD, but I am a little confused about some of the process.

I have watched several videos and I understand the mechanical process of performing the surgery on my mac, and I see it as something like

  1. Disassemble the mac

  2. Remove the spinning hard drive

  3. (And here is the first question) Do I just leave the SATA connector flopping around in the HDD slot?

  4. Partially reassemble the mac

  5. Swap the fusion drive cache SSD for the 2TB SSD

  6. Finish reassembling the mac.

At this point I have seen it suggested that I re-install the macOS from the internet. I tend to agree with this idea, as this mac has seen a lot of software upgrades in the past and doing a fresh install will help clean out the cruft.

The next step would be restoring user accounts and data. Here I can see two possibilities, and I don't know what is the preferred technique:

  1. Individually restore the user accounts/data from the time machine backups I made prior to the surgery.


  1. Plug the HDD that I extracted from mac into a USB 3 enclosure, and use that to restore the user accounts/data. But for this option I don't know the relevance of the cache SSD. Is it just superfluous now?

reiterating my questions:

  1. After removing the spinning HDD, do I just leave the SATA cable flopping around?

  2. When restoring user accounts/data, should I just use my time machine backups, or use the spinning HDD I removed?

  3. If I use the spinning HDD to restore data, is teh fusion drive cache SSD relevant any more?


This is the process that I took, and what I noticed during the updating of my Mac Mini

  1. I opened my mac only enough to replace the SSD part of the fusion drive with the new SSD. I left the HDD part of the fusion drive in the chassis.

  2. After re-assembling the system, I powered it on and issued an Opt-Cmd-r recovery command via my Apple wireless keyboard.

  3. When the recovery dialog came up, I selected restore from the Internet and Monterey.

  4. The new SSD was the only option I had for an install location, so I selected that. (There was no option to format the new SSD, and after the fact I saw that it was formatted as APFS. I am not sure if this is how the SSD was originally formatted). Then the installation started.

  5. Then things got weird. The installation stopped and I was shown a screen that alternated between two different graphics. There was no text explaining what this all meant. After some thinking I realized that that these graphics were prompting me to turn on the power switch of either my keyboard or mouse. It seemed that at this point in the installation the installer had lost communications with the wireless keyboard and mouse. After hunting around I found a wired USB mouse, and plugged that in, and the installation continued.

  6. Eventually I got to the point where the installer asked about restoring data from some other source. I selected to restore from a Time Machine backup, and plugged in one of my TM backup disks into the USB port.

  7. I elected to restore 1 Admin and 1 non-Admin account. I was prompted to reset the password of the Admin account, and I selected a new password. But the installer created a new (temp) password for the non-Admin account, and suggested that I write it down. While I did do that, when the system was fully restored, the new non admin account password didn't work, and all I can think of is that what took to be a "l", was in fact a "1". In my opinion, the font used for the password was not very good. But not to matter as I could use the admin account to force a password reset.

  8. The installer then started recovering the data from the TM backups.

  9. The recovery process seemed to take a long time, although I noticed that it had found something like 1 million files to restore.

  10. Eventually it completed. I logged in with my admin account, did a password reset of the non-admin account, and then logged back in with the non-admin account.

  11. After all my emails were re-imported into Mail, I needed to re-enter the passwords for my email accounts in order to bring them online.

  12. There was a lot of files copied to a "relocation" folder that I need to check over (but not sure how to check them right now).

  13. The only thing that doesn't seem to be working is VirtualBox, but I expected that to happen due to needing a kernel driver to be installed.

  14. The HDD part of the fusion drive is showing as Not Mounted and Type: Unknown, Owners: Disabled. I may bring that online later.

  15. Once everything else was done, I noticed that there was an update to Safari available, so I installed that. Obviously Apple hasn't generated a new Monterey image since Safari was updated.

  • Why would you remove the HDD? I would just replace the SSD with a larger SDD. Install macOS on just the SSD. The HDD could be erased and used for backups or other uses that do not require the speed offered by the SSD. Commented Jan 9, 2023 at 19:45
  • @DavidAnderson That's possibility, but I have no idea what happens when I install the blank SSD and power on. Removing the HDD made sense to me, even if I didn't look forward to the surgery.
    – Peter M
    Commented Jan 9, 2023 at 19:52
  • I would probably do the following. 1) Backup the Mac. 2) Shrink the partition on the HDD and add a JHFS+ formatted partition to the end of this drive. 3) Install High Sierra to this new partition. Now after replacing the SSD you will still have a bootable Mac. You can now partition, APFS format and install macOS to the new SSD. Afterwards, you can remove the High Sierra partition from the HDD. Commented Jan 9, 2023 at 20:17
  • @DavidAnderson Why would I want to go back to High Sierra when I am already running Monterey? ;-)
    – Peter M
    Commented Jan 9, 2023 at 20:19
  • Any macOS after High Sierra requires APFS. Installing macOS in a single APFS partition on a HDD results in extremely slow performance. High Sierra can be installed to a legacy JHFS+ formatted partition. Of course if you choose, you can install Monterey to a single new APFS partition on the HDD. Commented Jan 9, 2023 at 20:35

2 Answers 2


This all centres around "Is a Fusion drive usable if it's been physically split?"
I used to think it was, but it really isn't, they're married in such a way that breaking the bond loses all data.


  1. May as well, it will make no practical difference so long as it can't foul any moving parts.

  2. Migrate from Time Machine, at first boot with your newly-installed OS. Don't set up accounts first, or you get doubled accounts & a data nightmare.

  3. Not applicable.

  • Side question then, with a fusion drive the SSD is not just a cache, but the data is split across it and the HDD. An analogy would be that you can't typically pull a single drive from a RAID system and use it.
    – Peter M
    Commented Jan 9, 2023 at 19:28
  • 1
    It is, in effect, a bit like a RAID 0. One working whole or two broken halves.
    – Tetsujin
    Commented Jan 9, 2023 at 19:29
  • Can you comment on what @DavidAnderson said about leaving the HDD in place? It sounds like braking the fusion drive in two would stop it from booting, and hence allow me to get away with less surgery.
    – Peter M
    Commented Jan 9, 2023 at 19:53
  • 1
    It's either leave the drive in place and have some spare storage (a 3rd Time Machine backup location for me!). Or perform all the extra surgery, remove the HDD, throw it in my spares box, and never touch it again. I'm voting for the easy solution! Of course either way I have an unused 128GB Apple SSD that I don't have an external enclosure I can use to re-format it.
    – Peter M
    Commented Jan 9, 2023 at 20:00
  • 2
    An 8 year old hard drive is not one I'd have a lot of confidence in, though.
    – benwiggy
    Commented Jan 10, 2023 at 9:13

Yes, there's no issue with having an internal SATA cable that's not connected to anything. (Alternatively, you could even swap in a 'standard' 2.5" SATA SSD for maximum capacity.)

To clarify the point: Fusion drives only work together. As soon as you remove one device (of if one of them breaks), then each single device is useless on its own and cannot be read individually. The SSD is not a cache: it contains data that isn't on the hard drive part.

  • I wonder if the SSD was removed, placed in a USB enclosure and plugged into an USB port on the Mac, then would the Mac boot? In other words, would the Fusion drive still work? Commented Jan 9, 2023 at 21:06
  • @DavidAnderson It's certainly an experiment to be done! ;-) I think the days of Fusion drives are in the past, though Apple may well reuse the technology for other things. Back in 2012, I envisaged that iCloud might use it, so that your local storage is the fast, frequently used data; and the 'slow, large' part is actually cloud storage.
    – benwiggy
    Commented Jan 9, 2023 at 22:14
  • "The SSD is not a cache: it contains data that isn't on the hard drive part.". That all comes down to the definition of what a cache is. The Fusion drive combines two physical separate drives into one logical drive, and puts the most frequently accessed files on the SSD part. So the SSD is acting as a cache for the logical drive.
    – Peter M
    Commented Jan 9, 2023 at 23:37
  • 1
    @PeterM Potahto. I'd say that's a less helpful definition for understanding how it works, even if semantically possible. Caches usually involve temporary data that is duplicated from its original store. If you say "it's a cache", then people will think that the SSD is redundant. "Tiered storage" is a better fit than "cache".
    – benwiggy
    Commented Jan 10, 2023 at 7:53
  • 1
    I used to think you could split off the SSD because it was "just a cache", which was really a dangerous misconception. I now think of it more akin to a 'smart' RAID0; break the connection, both halves are gone.
    – Tetsujin
    Commented Jan 10, 2023 at 8:55

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