2/24/2023 0 Comments Diskmaker x reviewSuch boot drives are easy to create on your own, here are instructions for making boot disks for OS X 10.9, OS X 10.8, and OS X 10.7. This is a good example of why it’s very valuable to have a bootable USB thumb drive set up with whatever version of Mac OS X is running on your Macs, because without a separate boot drive some of these errors would be unresolvable. The above steps did the trick and everything was working again as expected. I ran into this twice recently, first when attempting to modify partitions on a drive, which came right along with a separate “ partition failed” error, and again was triggered when attempting to format those partitions. Now perform the original task that threw the “Couldn’t Unmount” error.Go to “First Aid” and verify the disk, then repair if needed.At the boot menu, choose “Disk Utility” (if using an Installer disk, pull down the “Utilities” menu to access Disk Utility).Hold down the OPTION key during boot, then select the attached boot drive (typically has an orange icon at the boot menu).Attach the USB boot drive to the Mac and reboot.You will need any Mac OS X boot drive to complete this task, I used a Mavericks boot installer drive for this purpose but others should work too, whether they are installation drives or just recovery drives, the important thing is they are bootable and separate from the primary boot disk that stores the installed OS: This is the recommended method because it should always fix the error. How to Resolve the Unmount Error with a USB Boot Drive We’ll also show you a way to forcibly unmount a disk by command line, though that approach must be used with caution as it can lead to data loss on the drive in question. We’ll cover both with a bit of explanation. This will allow you to fix the problem, regardless of the cause, by one of two means, the first is a sure-thing to fix the issue, while the other only works sometimes. For the boot drive, it shouldn’t matter which version of Mac OS X it’s for (assuming 10.7, 10.8, 10.9, 10.10, 10.12, 10.13, 10.14, etc at least), the only requirement is that it has Disk Utility – which they all do. For the former situation where the boot drive is being modified, the easiest solution is to boot from another drive and run Disk Utility from there instead. This involves completely erasing the internal HD and starting over with a clean disk- this is only possible with bootable media, and thus the benefit of creating a bootable USB.Typically the “Couldn’t Unmount Disk” error pops up when the currently boot drive is being modified, or if a disk was trying to be erased you may find the erase failed with a couldn’t unmount disk error. A clone, on the other hand will only be a clone if you concientiously and continually re-clone your ever-expanding HD.Ģ) The bootable USB stick is useful for doing a clean install on a Mac. This is not a 'clone', but you will be able to restore your most recent system state (as of the last backup) if your internal HD fails. (or got to the Time Machine preferences in your system prefs and select the external HD). Connect an external HD- and you shoudl get a popup asking if you want to use this as your Time Machine backup. 1) The free Time Machine app systematically backs up your HD at regular intervals- all that is required is an external HD at least as big as (better is twice or more) the size of your internal HD. These are two completely different animals. You have conflated two seperate issues here:Ģ) creating a bootable OS X Install USB stick.
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