I am trying to partition my internal HDD so that I can install Windows 10. I tried using Boot Camp to do this (which is where I think the problem started) but it failed so I am trying to do it manually.

Now when I open Disk Utility it looks like this:

Disk Utility - Device View

When I then click partition the 'pie chart' adds up to 6TB, which is twice as much storage than I have:

Disk Utility - Resize Partition

When I try taking away the left hand partition and apply, it fails. If I add another partition, it duplicates that too.

When I look at storage in the 'About This Mac' tab it shows Macintosh HD twice, each HDD looks exactly the same.

Does anyone know why this might be happening?

Any help would be really appreciated.

My Mac info:

OS X El Capitan Version 10.11.6
iMac (27-inch, Late 2012)
Processor 3.4 GHz Intel Core i7
Memory 32 GB 1600 MHz DDR3
Graphics NVIDIA GeForce GTX 680MX 2048 MB
Storage 3TB SATA Disk

Output of sudo gpt -r show disk0 entered in Terminal:

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640  4293286064      2  GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
  4293695704     1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  4294965240  1565305744      4  GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
  5860270984      262144      5  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  5860533128           7         
  5860533135          32         Sec GPT table
  5860533167           1         Sec GPT header

Output of diskutil cs list entered in Terminal:

CoreStorage logical volume groups (1 found)
+-- Logical Volume Group D60F9C59-F78F-4DA6-A77E-BFCBAA1CCDE7
    Name:         Macintosh HD
    Status:       Online
    Size:         2999599005696 B (3.0 TB)
    Free Space:   0 B (0 B)
    +-< Physical Volume 4B824E44-314C-483C-8767-67B3C5006A65
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     2198162464768 B (2.2 TB)
    +-< Physical Volume 9BF5F397-185C-4561-B24B-D38C3C81442F
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk0s4
    |   Status:   Online
    |   Size:     801436540928 B (801.4 GB)
    +-> Logical Volume Family E8825944-F8B2-4073-8806-1B9B1FED716D
        Encryption Type:         None
        +-> Logical Volume 17FA23EF-79C7-41E2-A04B-AFA3F449624C
            Disk:                  disk1
            Status:                Online
            Size (Total):          2998978236416 B (3.0 TB)
            Revertible:            No
            LV Name:               Macintosh HD
            Volume Name:           Macintosh HD
            Content Hint:          Apple_HFS
  • i67.tinypic.com/33c85lz.png . I did the first aid on disk utility.
    – TeamPaul
    Oct 2 '16 at 9:22
  • Haha, sorry, I've entered it into the original post now. Thank you.
    – TeamPaul
    Oct 2 '16 at 9:40
  • Did you try to create a 800 GB partition in Boot Camp for Windows 10?
    – klanomath
    Oct 2 '16 at 9:44
  • I tried to make it 500 GB.
    – TeamPaul
    Oct 2 '16 at 10:00

I don't know the history of your iMac but your internal hard drive is pretty messed up.

The drive is partitioned to five slices:

  • the EFI partition at index 1 with a size of 209 MB
  • a Physical Volume at index 2 with a size of 2.2 TB
  • a Recovery HD partition at index 3 with a size of 650 MB
  • a Physical Volume at index 4 with a size of 801 GB
  • a Boot OS X partition at index 5 with a size of 134 MB

Additionally the device contains a Logical Volume Group (CoreStorage). CoreStorage is a logical volume manager, which is an additional layer between device/partition and a volume.

A Logical Volume Group is based on one or several Physical Volumes (which can be one or several physical devices/partitions) and may contain one or several Logical Volume Families/Logical Volumes.

  • On one disk the common layout of a LVG is: LVG < one PV (disk0s2) > one LVF > one LV (disk1).

  • On two disks (e.g a Fusion Drive) the common layout of a LVG is: LVG < two PVs (disk0s2 & disk1s2) > one LVF > one LV (disk2).

Your actual disk (disk0) has a non-standard layout: LVG < two PVs (disk0s2 & disk0s4) > one LVF > one LV (disk1). This may happen after resizing the CoreStorage stack and adding an additional partition in the then unallocated disk space, formatting it as HFS volume and adding it as a second Physical Volume to the already existing Logical Volume Group.

I can't really explain the origin of the Boot OS X volume (disk0s5).

To salvage the mess, backup Macintosh HD with Time Machine, boot to Internet Recovery Mode, repartition the internal drive to one (main) non-CoreStorage partition and restore the backup:

  • Booted to your main volume attach your Time Machine backup drive. Go to the menubar and initiate another Time Machine backup cycle by choosing "Backup now...".
  • Detach the Time Machine drive after the backup is done
  • Restart to Internet Recovery Mode by pressing alt cmd R at startup.
    The prerequisites are the latest firmware update installed, either ethernet or WLAN (WPA/WPA2) and a router with DHCP activated.
    On a 50 Mbps-line it takes about 4 min (presenting a small animated globe) to boot to a recovery netboot image which usually is loaded from an apple/akamai server.

    I recommend ethernet because it's more reliable. If you are restricted to WIFI and the boot process fails, just restart your Mac until you succeed booting.

    Alternatively you may start from a bootable installer thumb drive (Yosemite or El Capitan) or a thumb drive containing a full system (Yosemite or El Capitan).

  • Open in the menubar Utilities/Terminal

  • Enter diskutil cs list
  • You will get an identical output as in your question
  • enter diskutil cs delete lvgUUID (with lvgUUID: the UUID of your Logical Volume Group). In your case that's diskutil cs delete D60F9C59-F78F-4DA6-A77E-BFCBAA1CCDE7.

    The command should delete all CoreStorage items.

  • Enter exit in Terminal
  • In the main Recovery Mode Window open "Disk Utility"
  • Choose the main disk (not one of the volumes!) and hit the Erase button.
  • Repartition the main disk to 1 partition, OS X Extended (Journaled) and GUID partition map.
  • Attach your external Time machine backup drive
  • Quit "Disk Utility" and open "Restore from Time Machine". Choose the external drive as backup source and restore the latest Time Machine backup on your empty internal drive.
  • After restoring the backup, quit all apps and reboot to your main drive.
  • I'm trying to work out when all of this could have happened. The first time I've changed the internal HDD in any way was when I used Boot Camp yesterday. When the partition failed I used Boot Camp to restore it to one partition, then I tried to partition it through Disk Utility (where it was already showing two identical Macintosh 3 TB HDDs) which is where it must have split it up further in a weird way. I'm not too sure how to carry out your suggestion of booting to internet Recover Mode, also, I made a backup to time machine before I used Boot Camp, do you think this backup will suffice?
    – TeamPaul
    Oct 2 '16 at 15:51
  • No, I bought it new from apple. I did receive an email from apple to say the hard drive in my Mac needed replacing as could be a problem with it, but I missed the date to get this fixed and the hard drive hasn't failed so I thought it was fine but maybe this has something to do with it? This is the link to the apple page about the hard drive replacement program. apple.com/uk/support/imac-harddrive-3tb
    – TeamPaul
    Oct 2 '16 at 16:03
  • @TeamPaul I have an idea how the misery happened: a 2.2 TB start block limit may exist in the MBR. Then even after entering only 500 GB in Boot Camp Assistant (with a start block in the 2.5 TB range) the size of the Win partition will be extended to ~800 GB to keep the start block in the 2.2 TB limit.
    – klanomath
    Oct 2 '16 at 16:08
  • Shall I try booting to internet recovery mode then? Do I go on disk utility from this menu and then delete any partitions that are there to create one whole disk? Or shall I erase disk and do complete reinstall then recover files from time machine?
    – TeamPaul
    Oct 2 '16 at 16:12
  • I'm happy to wait, thank you for taking all this time to help me with this. Yes a how-to would be quite useful! Thank you
    – TeamPaul
    Oct 2 '16 at 16:19

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