Disk locked? Won't unmount? Cannot reinstall OS?

[DennisO92]

I want to erase an old hard drive but have run into the issue of being unable to erase it with disk utility in recovery mode. I get the error that the disk will not unmount and trying to reinstall the OS without erasing it just leads me to this:

 

[FarmerBob]

I'd try using DiskUtility to Erase/Reformat first. That's probably the only way to do it. Now you can probably use/access DiskUtil in the installer to do it. Without have to completely back out of the installer . . .

 

[DennisO92]

Using disk utility to erase/reformat the drive fails and says that it could not unmount the disk.

 

[dsemf]

Using disk utility to erase/reformat the drive fails and says that it could not unmount the disk.

You need to use internet recovery or a bootable disk instead than the recovery drive.

DS

 

[FarmerBob]

That's too bad. In the "old days" it use to be "the go to" app to fix anything. I have noticed that it's gotten weak over the years.

In your case when I had things like this happen, it was pure luck most of the time. There are a ton of apps out there, but which one . . . I have used Drive Genius and Disk Warrior for years that have worked when I needed a fix. Even recently to fix a "Trash Can". But truthfully, drives are a dime a dozen, since I have a boxes of them, and a smaller drive like that are not all that expensive. Even larger drives are inexpensive. So . . .

Good Luck!

 

[TheSkywalker77]

I'm not an expert when it comes to these things, but did you have FileVault on?

That may not even be the problem, but it seems like that could cause this.