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:

How to make a vertical laptop stand from laser-cut acrylic

When my wife is working from home, she likes to sit at a proper desk with a monitor, keyboard, and mouse instead of hunching over her laptop. To make it easy, I set up an "umbilical cord" of power, USB, and display connection to plug in and off she goes. To free up room on her desk she lays her 13" Macbook Air on the floor which is always kind of awkward. To resolve this, I thought a space-saving vertical laptop stand could help, much like one of these made by Twelve South or Rain Design.

But it's no fun to buy one; let's design and build one from scratch out of laser-cut acrylic!

The two copies of the laptop stand I cut out of acrylic

How to Install a Fusion Drive into a Mac mini Running Mavericks

In order to speed up my computer without the expense of a large SSD, I just finished installing a DIY Fusion Drive into my 2011 Mac mini with great success. (This should work for Yosemite as well with minor modifications). I didn't expect the need to write about it but there were enough lessons and deviations that I'll describe them. Originally the Fusion Drive was released using Mountain Lion so most write-ups have not been updated for the newer OS X Mavericks. 

Update 10/24/2019: See also my post about setting up a proper recovery partition and fixing macOS installation errors.

Assumptions: You have a working 2011 Mac mini running OS X Mavericks with a single HDD and want to install a second drive (an SSD) internally to make a Fusion Drive.

First, the hardware, which I ordered all from Amazon. I chose:

• Mac mini dual drive kit from iFixit ($30) because I liked the included tools better than the similar kit from OWC (note: if prices are wonky, just order from the manufacturer directly or choose the other brand)

• Samsung 840 EVO 120GB SSD, because it was on sale and had good reviews
• That drive is now discontinued, so you might consider the Samsung 850 EVO