Disk Erase failed with the error: Couldn't unmount disk

[defmuse]

I have lost my original Mountain Lion install discs. Am running a MacBook Pro (2011 model).

I found a couple of articles that show you how to erase & reinstall everything without using physical discs. It involves restarting my MacBook, holding down Command+R, going to disk utilities, and using that to erase my hard drive

However, when I try to erase my drive, this error message pops up: "Disk Erase failed with the error: Couldn't unmount disk."

I've attached a pic of the error that pops up.

On the left hand side of the disk utility window (see attachment), where the hard drives are displayed, it shows the 500GB Toshiba MK drive. Directly below it, is the "Macintosh HD" option.

This error pops up ONLY when I try to erase the Toshiba drive. But it allowed me to erase the Macintosh HD option. Why is that? Has my drive been erased nonetheless? Or do I still need to do something else?

Thank you in advance for any help on this matter.

 

[IWT]

Hi defmuse

A warm welcome to Mac-Forums.

It's the Macintosh HD indent that you should devote all your energies to.

Erase the HD and allow the OS to download from the Internet. It may take a long, long time. Depends on your broadband speed, of course, but it still seems to take forever when you include the installation.

Any other queries, just let us know. I think you are on top of the situation; just remember it's the Macintosh HD you want.

Ian

 

[defmuse]

Thank you so much for your very quick reply, Ian - really appreciate it. Significant relief at my end. Now I just have to figure out how / the steps to downloading Mountain Lion via the net (net speed shouldn't be an issue for me). Much respect.

 

[IWT]

A pleasure to help.

This linked article may be of some assistance.

http://osxdaily.com/2014/12/14/reinstall-os-x-mac-internet-recovery/

Ian

 

[defmuse]

Thanks a lot, Ian.