Fixing a Mac Fusion Drive that Disk Utility can’t erase

My Mac Mini w/ Fusion Drive (that’s a hard disk and an SSD pretending to be a single volume for better performance) froze and wouldn’t boot. Nothing would make it boot normally again. Recovery mode was OK but couldn’t erase the boot volume nor mount it via Disk Utility (I just got “Unable to delete the core storage logical volume”), so reinstalling seemed impossible.

Fortunately, I figured out how to do it, using some help from a StackExchange post I found. See below for the details.

The magic incantation that fixed it was inspired by instructions I found here:
http://apple.stackexchange.com/questions/136590/how-can-i-delete-a-partition-corestorage-logical-volume-from-the-terminal

 

Note: THIS WILL WIPE YOUR HARD DISK. Only do this if you’re completely ready to just burn it all down to the ground and start over with a blank boot disk.

 

Here are the steps:

  1. Boot the recovery volume, which will take you to an OS X Utilities page that shows four options: “Restore From Time Machine Backup”, “Reinstall OS X”, “Get Help Online”, and “Disk Utility”. If you have gotten to this article you have probably already been into Disk Utility a few times already without success, so don’t open Disk Utility.
  2. From the Utilities menu of the “OS X Utilities” app, open Terminal. (Maximize the terminal window that opens so it’s easier to see the output of the next step.)
  3. Run diskutil cs list . Using the mouse, copy the long alphanumeric string that’s on the third line of output after “Logical Volume Group”. That’s the Logical Volume Group’s universally unique identifier, a.k.a. its “lvgUUID”.
  4. LAST WARNING: FROM HERE ON OUT THIS DELETES ALL OF THE DATA ON THE HFS+ LOGICAL VOLUME (but it doesn’t delete the recovery partition).
    Run diskutil cs delete FOO-BAR-BIZ-BAZ, where FOO-BAR-BIZ-BAZ was your lvgUUID. This deletes the logical volume group. diskutil will print things about erasing the physical partitions that made up the logical volumes, which in my case were /dev/disk0s2 (a 931GB partition on the internal hard disk) and /dev/disk1s2 (a 113GB partition on the internal SSD). Pay attention to the names of the devices that it just liberated on your system, since you’ll use those device names in the next step.
    At this point you have two empty HFS+ partitions that are not a Fusion drive anymore, so you’ll want to rebuild the LVG from those two physical partitions.
  5. Run this: diskutil cs create 'Macintosh HD' /dev/disk0s2 /dev/disk1s2 and adjust the /dev/.. stuff to include the partitions that diskutil said it erased & mounted in the prior step.
    On my Mac Mini it took about a minute to finish.
    At this point if you run diskutil cs list you should see just a Logical Volume Group and as many Physical Volumes as you added (which is two in my case, disk0s2 and disk1s2), without any Logical Volumes yet.
  6. Quit Terminal.app and run Disk Utility from the main “OS X Utilities” app.
    Disk Utility should show “Fusion Drive” without any partitions in it, which is expected since we just created the Logical Volume Group without any Logical Volumes in it.
  7. Select the Fusion Drive and run First Aid on it.
    First Aid will immediately create a Logical Volume and format it, leaving one big partition of type”OS X Extended (Journaled)” named “Untitled”.

Now you’re free to do whatever you want with this empty disk. In my case, I erased it and created a new partition named “Untitled” of type “OS X Extended (Journaled, Encrypted)” since I want full-disk encryption.

(I tried to call it “Macintosh HD” during the erase step, but Disk Utility failed to erase the disk and complained that name was invalid, so I just left it as “Untitled”, erased the disk, and then renamed it by selecting the Untitled volume in the left-hand-side list of devices, then clicking on the right-hand-side pane where the name Untitled was shown and editing it there.)

After this, I quit out of Disk Utility, and ran the “Reinstall Install OS X” app. That does a network install which first required me to log in with my Apple ID and then downloaded the install files.

 

25 thoughts on “Fixing a Mac Fusion Drive that Disk Utility can’t erase”

  4. Thanks for your tutorial. It didn’t quite work for me. I had to delete it in the terminal, but then recreate it in the DiskUtility without doing anything else in the terminal.

  5. i am only able to see my toshiba hd with disk0s1, disk 0s2, diskos3 and disk0s5 but nothing underneath it as you described. does that mean my hd is failing?

  6. Thanks so much! Been trying to work this out all day. Yours is literally the only solution that works!

  8. These instructions just saved me. I have an 4K iMac from work that failed after an macOS point update and wouldn’t let me reinstall or reformat the drive. Thank you for taking the time to explain these steps and posting them.

  10. YOU, SIR, ARE A GENIUS.

    I’ve been poking around the internet for two days trying to figure this thing out.

    Your solution worked like a charm.

    THANK YOU AND ALL HAIL!

  11. Mac Senior tech could not help me, but I found this and it worked!! Thank you!! iMac 27″ 2012 model

  12. I tried to do this. When i run diskutil cs delete FOO-BAR-BIZ-BAZ I get this message: FOO-BAR-BIZ-BAZ (with my string) does not appear to be a valid Core Storage Logical Volume Group UUID or name.

    What to do nooow?

  13. I tried this. When I run: “diskutil cs delete 0835A41A-8861-4A20-8E2E-BF7A027E7D6C”, I get the message: “0835A41A-8861-4A20-8E2E-BF7A027E7D6C does not appear to be a valid Core Storage Logical Volume Group UUID or name”. What to do?

  14. After running: “diskutil cs deleteVolume 0835A41A-8861-4A20-8E2E-BF7A027E7D6C” found on another guide I got this message: “The Core Storage Logical Volume UUID is 0835A41A-8861-4A20-8E2E-BF7A027E7D6C
    Started CoreStorage operation on disk2 Macintosh HD
    Unmounting disk2
    Error: -69888: Couldn’t unmount disk”

  15. Jamie,

    *Thank you* very much for posting this useful info. Your guidance worked wonders. Clear documentation. Got my Fusion drive working properly again.

    Much appreciated.

  16. You have no idea how happy I am I stumbled across this article. Been without my iMac for months because I didn’t know what to do and couldn’t afford for Apple to make me pay to fix it!

    I’ve been through it all with them and all I needed to do was google!

    Thanks so much!!

  17. 10.14 “Mojave” comes with a new diskutil command, resetFusion, that does it all in one step.

  18. Hi Jamie, I just wanted to let you know that this is still incredibly useful – the only solution I could find anywhere that actually did the trick. I’ve been stuck on Sierra for a year thanks to having a fusion drive.

    Now that Mojave’s out it was time to try again, and I can’t tell you how thrilled I am to actually have a working computer running the latest and greatest again.

  19. My restoration from TimeCapsule was stuck while erasing the destination Fusion disk. These instructions were excellent and fixed the problem. Thank-you to Jamie Flournoy.
    I recommend adding a small correction in step 6 because my empty Fusion disk was hidden: change the View in Disk Utilities to show all disks (not just volumes only).

  20. Hi,

    thank you for the guide! It saved me.
    Otherwise I had also to do the command:

    diskutil cs createVolume “logicalvolumegroup” jhfs+ ‘Macintosh HD’ 100%

    where logicalvolumegroup is the new lvgUUID created.

    This because when I try to launch the SOS recovery on the Fusion Drive it remain stucked without doing anything, so I created the volume in the terminal.

  22. Amazingly helpful article and, like so many of the other comments here, this is the only solution that I could find that actually worked. My Mac Mini with fusion drive is up and running again – thanks so much.

  23. PERFECT !!! my ‘diskutil resetFusion’ command in Terminal didn’t work, I was showing two blank drives (1TB rotational and 32GB SSD) I needed to run ‘diskutil cs create ‘Fusion’ /dev/disk0s2 /dev/disk1s2′ then run FirstAid… after that it was a simple restore and done :) THANKYOU !!!

  25. Great article, you saved me.

    Only change was DiskUtil didn’t show thew new fusion drive so like Gio I had to use command below in terminal to create the Fusion volume and format it.

    diskutil cs createVolume “logicalvolumegroup” jhfs+ ‘Macintosh HD’ 100%

    where logicalvolumegroup is the new lvgUUID created.

    Many thanks!

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