PC formatted drives with a GPT partition, will cause the Disk Utility to produce the error. When I click 'details' it says: 'The volume Macintosh HD on disk2s5 couldnt be unmounted because it is in use by process 677 (kextcache). When formatting an external drive from macOS 10.11.x (El Capitan) and macOS 10.12.x (Sierra), and 10.13 (High Sierra) Disk Utility the follow error may occur, MediaKit reports not enough space on device for requested operation. If you want your Mac to start up again from the volume you've just erased, select Reinstall macOS in the utilities window, then click Continue and follow the onscreen instructions. Hi, Im trying to completely reset my Mac Pro by using Disk Utility in Recovery Mode but get the following error message when I click on erase Macintosh HD: 'Erase process has failed.When you've finished, close Disk Utility to return to the utilities window.What should I do Either make the encryption in FileVault to continue the progress which didn’t work after reading about it and trying things or to erase the HD and start a new install from my Time Machine backup. Optional: if you used Disk Utility previously to add internal volumes other than Macintosh HD, you can erase them individually using the same process. When erasing it says Erase process has failed with details saying Couldn’t unmount disk - Operation failed.If you can't see this button, click Erase instead. At this point, you can try solving it with Recovery Partition. Format: APFS or Mac OS Extended (Journaled), as recommended by Disk Utility If the error message appears during 'First Aid' or formatting a non-boot disk, the above means will not make effects surely.Click the Erase button in the toolbar, then enter the requested details:.Select Macintosh HD in the sidebar of Disk Utility.After that, type diskutil list to get a list of all the discs on the Mac. From the utilities window, select Disk Utility and click Continue. To begin, you must open the Terminal application.

If asked, select a user you know the password for and enter their administrator password.Start up from macOS Recovery: turn on your Mac, then press and hold Command (⌘) and R immediately until you see an Apple logo or other image.

Disk utility erase process has failed