Thursday, October 24, 2019

Mac High Sierra fresh install errors on DIY Fusion Drive

As a follow-up to my installation of a DIY Fusion Drive on the 2011 Mac mini, there are some clarifications that have become useful a few years later on. I wanted to reformat the drives with a fresh operating system to pass along the computer to a family member, but was getting errors during installation.

The bottom line is that the install process does not work on a freshly-created Fusion Drive, but you can get around this by restoring a Time Machine backup onto the new Fusion Drive. Along the way, I discovered how to make a DIY Fusion Drive with a properly working recovery partition for troubleshooting in the future. The 2011 Mac mini only supports up to macOS High Sierra, though I suspect this is all resolved in Mojave/Catalina thanks to the luxuriously simple "diskutil resetFusion" command that I was able to use on a 2014 machine.

The issue is that the macOS High Sierra installer will give errors when doing a clean installation on a DIY Fusion Drive system, reporting either “macOS could not be installed on your system - invalid request” or “the installer resources were not found”. I got nervous because I was already in Recovery mode and a fresh install was failing... was the computer just toast now?!?

First comes the "invalid request" error
And if you reboot, you get "the installer resources were not found"
It turns out that the solution is to split the drives up, do a regular install onto the hard drive, use that to create a Time Machine backup, then rebuild the Fusion drive, and restore the backup (i.e. NOT a new install). Phew! (Thanks to this thread for pointing me in the right direction.) OK let’s do this in detail:

To make a fresh install of macOS High Sierra on a DIY Fusion Drive:

  1. Create a High Sierra installation disk. I used this link to download High Sierra from the App Store, then these instructions from Apple to make a bootable drive.
  2. Boot up from the drive by starting the computer and holding down the option key
  3. Split up / sever the Fusion drive by following this guide from Macworld.
  4. Perform a fresh macOS install onto the HDD (not SSD) so that it stays as an jhsf+ (macOS extended journaled) volume.
  5. Boot the computer as normal and do the basic setup steps as per any new Mac. Everything should be like a typical system, except the parts of the Fusion drive will appear as two separate disks.
  6. Back up the system using Time Machine
  7. Boot up into Recovery mode (cmd-R)
  8. Re-create the Fusion drive using these instructions from Apple
    1. EXCEPT, in order to preserve the recovery partition on the new setup, do not choose the entire HDD for the Fusion terminal commands, just the large partition of it for storing data. For example if the HDD is "disk1", the large partition is probably something like "disk1s2". See here for details, and also see some background theory.
  9. Restore the machine from a Time Machine backup (NOT a fresh install)
When I did this the first time, I did not properly create the recovery partition and got errors later on when installing security updates. So this has me wondering if the whole reason the original OS install had errors was because it couldn't find the UUID of the recovery partition... but that's an exploration for some other time. If you're about to try this procedure, do us all a favor see if a fresh install actually works when creating the Fusion Drive as above (i.e. with the recovery partition). Let us know how it works out in the comments below!

It turns out I accidentally avoided this whole issue with my original Fusion drive installation because I simply restored the full system from a backup like I had intended. (Funny, I probably never had a recovery volume.) But for a fresh install, we need to follow the above steps.

Note that the above procedure was basically all the software steps needed to install a Fusion Drive to begin with. It’s nice that Apple’s documentation has caught up with this need, but unfortunate that it was not precise enough to recreate a proper Fusion Drive on High Sierra.

Has it worked for you?


  1. Holy Cow, man. You just saved my ass!

    We had a user accidentally update to Catalina -- which as you might know, partitions the physical hard drive into a system partition and user partition (for read/write security on core system files, presumably) and also kills all 32-bit apps, as they are officially unsupported on Catalina and up.

    Well, I formatted the drives and killed the partitions, and lo' and behold, I had two drives. A 28GB SSD and a 1TB HDD. I realized I split up the Fusion Drive! So I rebuilt the fusion drive via the terminal, and attempted to re-install High Sierra.

    Failure after Failure. I was feeling hopeless - then I stumbled upon this page via Google search. So awesome! Thanks for taking the time to detail this, people like you rock!

    Side-note, when I first created the Fusion Drive, I saw no recovery partition, so I'm not so sure if it would work without doing the steps you mentioned. This really seems like a weird specific case when we re-create broken fusion drives? Hmmm... maybe someone else can shine some light.

    Take care, and thanks again!

    1. Amazing! So glad I could help! Indeed, following the instructions exactly from Apple leaves the system without a recovery partition. Maybe eventually someone will fill us in if that was the ultimate issue or not.


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