How to Fix a “Could not Unmount Disk” Error on Disk Utility for Mac Guide

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Disk Utility usually works fine, but a frustrating Disk Removal Failed error can stop all attempts. This can happen during partitioning, disk check and repair, and even during formatting, and usually provides little or no additional information about how to fix the problem or even the problem with the error message or the application in Mac OS.

The “Disk Removal Failed” error occurs when the current drive is changed, or if an attempt was made to remove the disk, you may find that the removal failed when the disk error failed. In an earlier case where the boot drive is modified, the easiest solution is to boot from another drive and run Disk Utility from there. Regardless of the version of Mac OS X on the boot drive (assuming at least 10.7, 10.8, 10.9, 10.10, 10.12, 10.13, 10.14, etc.), the only requirement is that Disk Utility has it – which they all do. This allows you to solve the problem regardless of the cause in one of two ways, the first is to fix it for sure and the second only works sometimes. We will deal with both with a little explanation. We’ll also show you a way to forcefully remove a disk from the command line, although this approach must be used with caution as it can result in the loss of data on that drive.

How to fix a disconnection error on a bootable USB drive

This is the recommended method because it should always correct the error. You need any Mac OS X bootable drive to perform this task, I used a Mavericks bootable drive for this purpose, but others should work too, whether they are installing drives or just recovery drives , the most important thing is that they are bootable and a separate primary boot disk that stores the installed operating system:

  • Connect the bootable USB drive to your Mac and restart it
  • Hold down the OPTION key during boot and then select the connected boot drive (usually there is an orange icon in the boot menu)
  • Select “Disk Utility” from the boot menu (if you are using the Installer disk, open the “Utilities” menu to access the Disk Utility)
  • Go to First Aid and check the disk, then repair if necessary
  • Now run the original task that threw the “Unable to remove” error.

I’ve come across this twice recently, first when I was trying to modify the status of the partitions that came right along with a particular “partition failed” error, and sent in again, when I tried to format these Partitions. The above steps did the trick and everything worked as expected again.

This is a good example of why having a bootable USB flash drive installed is very valuable no matter what version of Mac OS X your Mac is running, because without a separate bootable drive, some of the resolve these errors. Creating such bootable drives yourself is easy, here are instructions for creating bootable disks for OS X 10.9, OS X 10.8, and OS X 10. For older Macs with earlier versions of Mac OS X, all operating systems running OS X 10.6 or earlier. they have a SuperDrive drive, so they come with a bootable DVD that can serve the same purpose.

Use the Mac Recovery partition to fix disk utility errors

If the Unable to Uninstall error is being triggered by First Aid or formatting a non-bootable disk, you may be able to fix the error by booting from the recovery partition included with all newer versions of Mac OS X .This will not work if the error was started by trying to modify the startup disk using partitions or formatting, and you must use the above method with the startup disk.

  1. Reboot your Mac by holding down the “Option” key and selecting the recovery partition
  2. Select “Disk Utility” from the start menu
  3. Go to “First Aid” to check and repair the disk or go to “Remove” to format the disk

Again, if the error throw disk is the same as the main boot partition, which also has a restore, the above method may not work to fix the issue. In that case, you need to boot from a separate USB drive to fix the error.

Forcefully remove a disk from the command line in Mac OS

Another method uses the command line to force the disk to be removed, but this is not the best option due to data loss.

Care must be taken with this approach, as the forced removal of the disk may result in loss of drive data. Therefore, this is only suitable if you intend to format and wipe the disk yourself.

Type the following string from the Mac OS command line:

diskutil unmountDisk force / Volumes / DRIVENAME

Replace DRIVENAME with the name of the volume you want to delete, then press RETURN to force the drive to be removed.

If that doesn’t help, you can take this step further:

You may also need to align the disk with a device ID to push it, so you can search for the disk first:

disk list

Then when you find the corresponding disk in the tag (/dev/disk1, /dev/disk2, /dev/disk3, etc.), you can target the disk to remove it. In this example syntax, we use /dev/disk3 to forcefully remove the command line and use sudo, which gives the task administrator privileges:

sudo diskutil unmountDisk force / dev / disk3

Click go back and enter the administrator password to forcibly remove the disk from your Mac.

When you’re done, you can exit the terminal as usual.

Do you know of another solution that can fix the “Disk Removal Failed” error message from Disk Utility? Share your experiences and solutions in the comments below!

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FAQ: Fix “Could not Unmount Disk” Error in Disk Utility for Mac

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In this guide, I will discuss how to Fix the “Could not Unmount Disk” Error in Disk Utility for Mac, which is very helpful.

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