I moved all the data and formatted them, but I had the same issue come back on the Mirror version! I had another popup that the disk was read-only and needed to be formatted. Once they appeared, the popup came back saying they needed to be formatted. I could hear the disk 'rattling' (being accessed) for half an hour or so. It also took ages for them to appear after the reboot. They were sort of 'stuck' in repair mode in Disk Utility. The disks could only be mounted in read-only mode, as Yosemite said they couldn't be repaired and had to be formatted.Īfter trying a disk repair, I was only able to (un)mount the disks again by rebooting. Two WD HDs (one Mirror and one Elements) were suddenly corrupted. But before trying this method, make sure that the recovery drive is located in the drive (a separate copy of os installed on it).I had a similar issue recently, and it's a bit worrying. This fix has worked for many users, so there are high chances that this will work for you as well. Fix “Couldn’t Unmount Disk” Error with USB Boot Drive If the issue is still there, then assume that the error is caused by modifying the bootable disk. Once the process is finished, check if the issue has resolved. Or go to Erase in order to format the disk. Step 3: Visit First Aid and try to repair the disk. Step 2: A boot menu will appear, here, select to choose “Disk Utility”. Step 1: Restart your Mac while pressing and holding the Option key, and then select to choose Recovery partition. If that’s not the case, this fix is worth trying, here’s how to resolve the error with the recovery partition:

Mind you, this fix will not work if the error was caused by modifying the bootable disk while creating a partition or formating. Fix “Couldn’t Unmount Disk” Error with Recovery Partition Let there be any Mac OS X version as it doesn’t matter (assuming 10.7 to 10.14 and above), this error can be easily resolved only if Disk utility is present on the drive.Īnyways, let’s head towards the actual fixes.

Keeping the fact in mind that Disk Utility able to execute from the external drive, we can use it to boot Mac from another bootable drive. Good thing is that a valid solution is available that will help us to resolve the “Couldn’t Unmount Disk” Error on Mac. SEE ALSO iTunes Not Showing Album Artwork? Here's how to fix it.

Os x error could not unmount disk