Rebuild a fusion drive

Hi everyone.
In this tutorial, I’m going to show you how to rebuild a fusion drive.
I recently, upon fiddling a bit too far, screwed my iMac’s fusion drive. As often when I break my toys, I go through all seven steps of mourning:

  • shock: oh f$%k, it won’t boot anymore!
  • denial: I’m certainly missing something, let’s try again (and again, and again…).
  • anger then sadness: screw it! stupid computer! Aaaaaw come one, Apple will charge me bazillions to fix this!
  • resignation: ok, I tried everything, I’m really screwed!
  • acceptance and reconstruction: ok, let’s draw my best friend the Terminal and see what we can do…

Hopefully, every version on macOS comes with a handy set of commands that you can use to rebuild a fusion drive.

First thing first: restart in recovery mode. It might take a few tries, and my experience tells me that you’d better shutdown your computer first.

Once recovery mode is loaded, fire up a terminal from the menus:

os-x-recovery-mode

Then, type this:

This will show you all your disks/partitions. There might be a whole lot more than the one that really exists, but nevermind. You should at least have your hard drive as /dev/disk0 (a few Tb presumably) and your SSD as /dev/disk1 (here, a few Gb: 64, 128 or something close). We will there assume that /dev/disk1 is your hard drive and /dev/disk1 is your SSD.

First, we need to recreate a logical volume group:

This will tie together the hard drive and the SSD. Then, we need to create a logical volume (ie: a partition) within that volume group:

Tadaaa, you’re done! Back into Disk utility, you should see your Fusion Drive back! Now all you have to do is reinstall a fresh copy of your prefered OSX/macOS version!