I have a 2014 iMac Retina running OS X Yosemite and a 3TB Fusion drive. I am attempting to restore it from a Time Machine backup, but when I try to do so, I get the error message, "The disk can't be erased." referring to the Macintosh HD Fusion drive. Trying to use disk utility to delete the drive also doesn't work.
I had previously had this problem when I had to restore my computer, and managed to use the solution found here using Terminal to manually delete the Logical Volume Group. However, now when I use the command:
diskutil cs deleteLVG UUID
The process begins and says "Destroying Logical Volume Group" but it only gets to 20% and then nothing happens. Even after letting it sit for hours it shows no further progress.
I also found this solution here, which recommends using the command
diskutil cs deleteVolume UUID
to delete the Logical Volume first, prior to deleting the Logical Volume Group, but when I do so I get the following message:
Error: -69779: Unable to delete the CoreStorage Logical Volume
So at this point I'm stuck. If anyone has any other suggestions for how I can delete the Fusion drive and restore from my Time Machine backup, I would appreciate any help. Thanks.
Best Answer
If all other means fail to remove a CoreStorage Volume Group you can always use
gpt
to remove the CS partition (or the CS partitions if it is a Fusion Drive).Preparation:
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 into 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 (preferably Yosemite or El Capitan) or a thumb drive containing a full system (preferably Yosemite or El Capitan). If you boot to a full system and login as admin you have to prepend
sudo
to execute some commands likegpt ...
ornewfs_hfs ...
!Modify the GUID partition table and replace your current LVG
diskutil list
andgpt -r show /dev/diskX
(with diskX: the disk identifiers of your internal disks (probably disk0 SSD/disk1 HDD) to get an overview. In the commands below I assume the disk identifiers are disk0/disk1.To delete a partition use:
Usually the Physical Volumes of a Fusion Drive have the index number 2:
Re-add the partitions with the same start block and sizes as they had previously
Format the new partition:
Create a new Logical Volume Group (or "Fusion Drive"):
Create a new Logical Volume:
or
To quit Terminal enter:
and quit Terminal
Open Disk Utility to verify the new LVG/LV