MacOS – Can’t delete the main Mac hard drive

disk-utilitymacbook promacos

I want to downgrade from macOS Sierra to OS X Mavericks. I have backed up my Mac using Time Machine and I made a USB with the OS X Mavericks Installer.

The thing is that when I reboot my Mac with Alt/Option, enter the USB Installer and open Disk Utility I can't delete the main drive since there isn't just the button to erase it, but the volume ("Macintosh HD") has this button. How can I solve this problem?

Best Answer

If your volume is 'formatted' with coreStorage as a logical partition, reverting might be enough to resurrect the "Erase" tab. In Terminal run the following command:

diskutil cs list

Note the disk identifier for the logical volume (e.g. on a Mac with only one drive and nothing else attached, it would be something like disk1)

Now try and revert from coreStorage (replacing disk1 with your own found disk identifier):

diskutil cs revert disk1

(you can run this either booted from your usual volume, or the installer disk)

If successful it will be mentioned in Terminal and the "Erase" button should have returned in Disk Utility, when you're booted from your installer drive.
(With more drives connected, make sure the disk identifier is the right one for the logical volume you want to revert)

If you can't successfully revert, make sure File Vault and encryption have been disabled, then try by destroying the whole coreStorage group with this command:

diskutil cs delete lvgUUID

replace lvgUUID with the UUID you found earlier in the diskutil cs list command under "Logical Volume Group".

Related Solutions

MacOS – Attempting to revert to Mac OS X Mavericks, now can’t get out of OS X Utilities!

Restart your Mac to Recovery Mode by pressing cmd R at startup
Launch Terminal from the menubar Utilities->Terminal

Enter the following command at the Terminal prompt:

defaults write com.apple.DiskUtility DUDebugMenuEnabled 1

Press enter
Quit Terminal
Start Disk Utility and enable Show every Partition in the Debug menu
After a few seconds all partitions should be visible
Activate the partition Macintosh HD if it's present and greyed out.
Erasing/formating of Macintosh HD should be possible now.

If this doesn't work quit Disk Utility and according to this site

Start Terminal and enter following command at the Terminal prompt:
```
diskutil cs list
```
This will give you a list of the CoreStorage volumes on your system. Your old FileVault 2-encrypted drive should be the only one listed.
Copy the Logical Volume Group (LVG) alphanumeric UUID of your CoreStorage volume. The LVG should be the first UUID listed and it’s the one you want to delete.
Next, run the following command:
```
diskutil cs delete lvgUUID #replace lvgUUID here by the UUID you found above
```
This will delete your CoreStorage volume and reformat it as an unencrypted HFS+ volume.

If it's still impossible to erase Macintosh HD or if it's not present consider the Internet Recovery Mode or a USB Recovery drive and format the whole internal drive.

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 the recovery netboot image which is loaded from an Apple/Akamai server.
In the opening window choose Disk Utility and format/partition the internal drive. Choose Mac OS Extended (Journaled) and GUID partition table (available with the Options... button). Quit Disk Utility.
Plug in your Time Machine backup drive.
Start Time Machine and recover your old system

MacOS – Can’t Delete Partition

Another cause of the "minus" button being greyed out in Disk Utility is that it doesn't allow you to delete the first partition on the disk.

Best Answer

Related Solutions

MacOS – Attempting to revert to Mac OS X Mavericks, now can’t get out of OS X Utilities!

MacOS – Can’t Delete Partition

Related Question