I created a fusion drive on my MacBook Pro running Mountain Lion and it worked like a charm for a while, but it somehow got corrupted.

Now I am unable to reformat or repartition the whole thing.

> diskutil cs list

CoreStorage logical volume groups (1 found)
+-- Logical Volume Group 40B334F6-6988-4727-9A2B-48E7999F4047
    Name:         MacintoshHD
    Size:         558926610432 B (558.9 GB)
    Free Space:   135995392 B (136.0 MB)
    +-< Physical Volume AC91E9F8-CAAA-48B9-A000-93E559F5D2DD
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     59162722304 B (59.2 GB)
    +-< Physical Volume 1319D374-879E-418F-88EF-5AA163B4105C
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk1s2
    |   Status:   Online
    |   Size:     499763888128 B (499.8 GB)
    +-> Logical Volume Family 3E85E6B1-4E99-4CBD-A34E-E720A090F373
        Encryption Status:       Unlocked
        Encryption Type:         None
        Conversion Status:       NoConversion
        Conversion Direction:    -none-
        Has Encrypted Extents:   No
        Fully Secure:            No
        Passphrase Required:     No
        +-> Logical Volume 76A3020B-B3C2-4905-9E09-2EBB5470261C
            Disk:               disk2
            Status:             Online
            Size (Total):       556000083968 B (556.0 GB)
            Size (Converted):   -none-
            Revertible:         No
            LV Name:            HD
            Volume Name:        HD
            Content Hint:       Apple_HFS

> diskutil cs delete 40B334F6-6988-4727-9A2B-48E7999F4047

Started CoreStorage operation
Ejecting Logical Volumes
[ \   \   \   \   \   \   \   \   \   \   \   \   \   \   ]

I remain stuck there and cannot delete the Logical Volume Group, or do anything at all on it's components.

By now I would be satisfied if I could just wipe /dev/disk0 and /dev/disk1 completely and start over, but unfortunately this does not work either :

> diskutil zeroDisk /dev/disk0

Started erase on disk0
Error: -69879: Couldn't open disk
Underlying error: 16: POSIX reports: Resource busy

I hope someone will be able to help me, I have absolutely no idea how to recover this computer!

I also posted this question on Apple's forums, but I expect a better answer answer and more importantly a longer shelf life!

3 Answers 3


I was able to delete a mess I made trying to delete my Raid 10 in diskutil (which ended up looking similar to above) using the commands below in Terminal.app. May or may not work with fusion but it's easier than booting up again.

Get rid of the volume - copy paste the logical volume name where it says "Logical Volume Name", without the quotes:

diskutil cs deleteVolume "*Logical Volume Name*"

Free the disk - copy paste the volume name where it says "Physical Volume Name", without the quotes:

diskutil cs removeDisk "*Physical Volume name*" 

Repeat these steps as needed.


I had a hard disk crash and, being under warranty, had to take it back to an Apple Repairer who installed a new hard drive. It was returned to me with Mountain Lion running fine. I proceeded to Restore from a Yosemite backup thence ran into a failure to boot (white screen a with circle with line through it). A verbose start (hold command-v on startup) reported Still waiting for root device.

Attempts to reinstall Mountain Lion would fail with something like No, you have a newer version of OS X already installed on that drive. Whilst attempts to reformat/erase with diskutil in recovery would harvest:

Disk Encryption Failed:
    Disk Encryption failed with the error:
        Unable to create a new core storage logical volume

I'm not sure how disk encryption fits into it because I certainly never used it, but I was stuck. Couldn't reformat the drive, couldn't install anything to it.

AppleCare was not helpful. The minions on the other end of the line read out all the nice and caring statements they were trained to do but at, at the end of the day, their best effort was "it shouldn't do that".

I suspect the root cause of my problem is that Mountain Lion cannot format the (fusion) drive in the way that Yosemite requires.

It took a couple of days to:

  1. install OS X (mountain lion) to an external drive
  2. boot to that
  3. download "Install OS X Yosemite" app
  4. Run that against the internal drive to reformat it and install yosemite
  5. Restore my backup

While I was unable to "cleanly" solve my problem, I managed to reset everything by booting in single-user mode from an external hard drive (reboot holding ⌘-S) and overwriting the disk directly with

cat /dev/random > /dev/disk0
cat /dev/random > /dev/disk1

Then I rebooted and I could reformat the drives (actually, I created another fusion drive using these directives).

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