I own an iMac late 2013 with a fusion drive. Recently I installed Windows 8.1 using Bootcamp on a separate partition on my disk. After a few days, the booting process of OS X started failing and I had to reinstall OS X. I decided to remove the bootcamp partition and start with a fresh installation.

It turned out that my fusion drive (128GB storage) and normal hard disk (1TB storage) were separated so I searched on how to fix this. I'm unable to find the tutorial which I followed back since it is some time ago. Currently, my iMac is quite slow and I was thinking that it might not be using the fusion drive. After running an iostat -d 1 command while writing some data to the disk, it turned out that my fusion drive is not writing anything:

      disk0           disk1 
KB/t tps  MB/s     KB/t tps  MB/s 
4.05   0  0.00    30.48 526 15.64 
0.00   0  0.00     9.70 429  4.07 
0.00   0  0.00     6.12 328  1.96 
0.00   0  0.00     6.99 395  2.70 
0.00   0  0.00     8.64 332  2.80 
0.00   0  0.00    10.09 480  4.73 
0.00   0  0.00   102.38 622 62.18 
0.00   0  0.00    97.81 392 37.49 
0.00   0  0.00    81.03 248 19.66 
0.00   0  0.00    88.55 454 39.29 
0.00   0  0.00   237.50 329 76.37

Note that disk0 is my fusion drive and disk1 is my normal hard disk as can be seen in the output from diskutil list:

    /dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *121.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Schijf                  121.0 GB   disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3
/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage Schijf                  999.3 GB   disk1s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3
/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Schijf                 +999.0 GB   disk2
                                 Logical Volume on disk1s2, disk0s2

The output of diskutil cs list is the following (which I think is right since my fusion drive is part of the CoreStorage volume):

CoreStorage logical volume groups (1 found)
+-- Logical Volume Group 654B2807-197B-46D1-9919-B75C0290D33A
    Name:         Schijf
    Status:       Online
    Size:         1120333979648 B (1.1 TB)
    Free Space:   120722538496 B (120.7 GB)
    +-< Physical Volume B735648A-5545-4004-B9F0-C79F6ECF65EC
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk1s2
    |   Status:   Online
    |   Size:     999345127424 B (999.3 GB)
    +-< Physical Volume 6C227359-82B8-4406-BE71-B77B9BEC7F1D
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     120988852224 B (121.0 GB)
    +-> Logical Volume Family 82BD1896-F03C-4111-8A01-40EADC2D5E2D
        Encryption Type:         None
        +-> Logical Volume 7D5C38D3-6682-498B-A003-82580C9EC3D3
            Disk:                  disk2
            Status:                Online
            Size (Total):          998973898752 B (999.0 GB)
            Revertible:            No
            LV Name:               Schijf
            Volume Name:           Schijf
            Content Hint:          Apple_HFS

I'm not sure what's wrong here. I would like my fusion drive to work again since the current speed of my computer is quite slower than it was before. Can anyone point me in the right direction? Many thanks!

  • Do you have a backup of your data? – user24601 Jan 24 '16 at 19:14
  • I don't think your fusion drive is set up properly—a Fusion Drive is a combination of a spinning disk (your 1 TB disk) and an SSD disk. Your Fusion Drive should be 1TB+128GB large. – samh Jan 24 '16 at 19:57
  • @user24601: I have a backup of my data but I would rather have a solution where I don't have to format my HDD. – Devos50 Jan 24 '16 at 20:40

If you have your data safely backed up or don't care about losing it, you can follow these instructions to recreate your Fusion Drive.

  1. Boot into Internet Recovery or an OS X bootable drive.

  2. From the Utilities menu, open Terminal.

  3. Run diskutil cs delete 654B2807-197B-46D1-9919-B75C0290D33A to destroy your current Fusion Drive. This WILL lose all of your data!

  4. Run diskutil list to get a list of the locations of your current drives.

  5. Run diskutil cs create <whatever you want to name your Logical Volume Group> <mount point of drive 1> <mount point of drive 2> to create a new LVG.

  6. Run diskutil cs createVolume <whatever your Core Storage LVG UUID, which you'll see in the last lines of the last command's output> jhfs+ "Macintosh HD" 100%>.

Now your computer should see a single virtual hard drive named Macintosh HD. Reinstall OS X on it and then you should be good to go. Good luck!

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Booted to your main volume or Recovery HD open Terminal and enter (El Capitan installed):

diskutil cs resizeStack 7D5C38D3-6682-498B-A003-82580C9EC3D3 1120g

or in (Mavericks/Yosemite installed)

diskutil cs resizeStack 7D5C38D3-6682-498B-A003-82580C9EC3D3 0g

Please add a comment if you get an error .

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  • When doing this, I get the following error: error -69771: The target disk is too small for this operation. Any suggestions? – Devos50 Jan 24 '16 at 20:39
  • El Capitan, the computer is a iMac late 2013. – Devos50 Jan 24 '16 at 21:09
  • Even 1050g is not working, guess I have to reinstall everything then... – Devos50 Jan 24 '16 at 21:26
  • I do not see the volume 'Schijf' in disk utility. In the left column of disk utility, I see: gyazo.com/666fc956482267497ddb2809ede1ef83. A verify of both of them yields return code zero. – Devos50 Jan 24 '16 at 22:44
  • Indeed strange but they both appear to be ok. – Devos50 Jan 24 '16 at 23:13

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