Have you ever met "partition failed couldn t unmount disk" or "erase process has failed" error on your Mac? How to fix it without data loss?

Recently, I have encountered some problems on my Mac, and it didn't allow me to repair the directory or permissions in Disk Utility. And an error "Disc couldn't unmount disk" or "erase process has failed." Why? This error can happen during partitioning, disk verification and repair, and even during formatting. What's worse, there's no additional information provided to solve the issue.

It still can fail to fix disk issues accompanied with some error messages, such as "couldn't Unmount Disk" or "erase process has failed." This error generally results from improper modification of the boot drive, such as partitioning, disk verification, or repairing or formatting. When this error pops up, not only will the Disk Utility halt suddenly, but the disk will suffer as well, such as damaged data on this disk. Therefore, it is imperative to resolve this error as soon as possible. Here we will share three solutions.
Methods to fix "couldn't unmount disk" error
1. Resolve with USB Boot Drive

If "Couldn't Unmount Disk" or "erase process has failed" error occurs, the simplest solution is to boot the Mac system and run Disk Utility on the disk. By this means, you can make use of USB boot drive.

1. First off, insert the USB boot drive to Mac and reboot.
2. Then, during booting, you should hold down the "Option" key button to select the attached boot drive.
3. Next, in the boot menu, select "Disk Utility."
4. After that, go to "First Aid" and verify the disk.
5. Lastly, perform the original task on the original disk.
2. Fix with Recovery Partition

If the error message appears during "First Aid" or formatting a non-boot disk, the above means will not make effects surely. At this point, you can try solving it with Recovery Partition.

1. For a start, reboot your Mac.
2. Then, when booting, hold down the "Option" key to select Recovery Partition.
3. Next, access Disk Utility from the boot menu.
4. Lastly, select "First Aid" to re-verify the disk or choose "Erase" to format the disk at your will.
3. Solve with Command Line

Moreover, you can also attempt to eradicate this error, forcing unmounting disk by command line. Follow the steps below:

1. To begin with, you have to access the Terminal application.
2. Then, input the "diskutil list" line, which will list out all the disks on the Mac.
3. At this time, you ought to find out the disk that you want to force unmount.
4. Lastly, you should type "sudo diskutil unmountDisk force /dev/disk" line. Replace the "/dev/disk" with the correct disk number, such as "/dev/disk1".

If you found your drive in unmounted condition on Mac and urgently need to recover the data, then recover them as below steps.

Read more? How to Fix "Couldn't Unmount Disk" Error