disk utility couldn't unmount disk

Question

disk utility couldn't unmount disk

Hi,

I have been having some problems with my iMac recently and I thought I would try to reformat my fusion drive and reinstall High Sierra.

I have created a bootable usb drive (10.13.2) and booted from it. In Disk Utility, I select the internal partition containing High Sierra (also 10.13.2), click erase, and after about 30 seconds it tells me that it cannot unmount the disk! I then tried booting from the recovery disk (Yosemite) and it cannot unmount the disk either!

Finally, I tried the 'Install macOS' option, but my internal drive is showing up as a drive that cannot be used to start up my computer!

Any help would be appreciated.

S

iMac, macOS High Sierra (10.13.2), 27 inch Retina Late 2014, 4.0 GHz.

Posted on Dec 26, 2017 12:53 PM

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Answer 1

Top-ranking reply

Kappy

Level 10

362,007 points

Dec 26, 2017 1:11 PM in response to Stuart Oliver

Boot from your USB bootable drive. Try repairing the disk in Disk Utility using First Aid. After doing that click on the Unmount button in the toolbar to see if the disk disappears from the Desktop. Continue with your plan if it does. If that doesn't work then quit Disk Utility and open Terminal from the Utilities' menu. At the prompt paste these lines individually pressing RETURN at the end of each line.

diskutil list

In the output, you should find your Fusion drive listed. Note the device information. It will appear similar but not the same as this: /dev/disk0s2. Use the device reference in this next command.

diskutil umount force /dev/disk0s2

Now, quit Terminal and run Disk Utility. Try formatting the Fusion drive now. To be sure you do this right, please observe that the drive may appear in the list as ghosted because it is unmounted. You might see that it is displayed on the list as:

Fusion Drive

Macintosh HD

Macintosh HD may not appear. In its place would be "disk0s2." It is this indented entry that you want to erase.

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