Using Disk Utility to Erase Disk-won't unmount

I have a MacPro and 4 drives inside it, one of which I need/want to erase. I have backed it up and using DU tried to erase it = by both highlighting the drive identifier and the name - in both cases, whether I try to erase disk or set it to erase to one partition, I get a message saying it can't do it because it can't unmount the disk.

I backed up my startup drive to this drive so I could wipe and reinstall OSX on my new SU drive but now I can't delete items off the backup drive [the one I want to erase] because the message says I can't delete backup items. And I can't erase the drive to get a brand new drive to work with.

I don't need the old SU material on this drive, it was just a way to be sure I had it before using Migration Asst to reinstall the SU on the new SU drive = I used SuperDuper to clone the old SU onto this drive - then I used Migration Asst to move the stuff back to the new startup drive = but now I want to EITHER get rid of the system files and apps [no need for those = I don't min

Mac OS X (10.7.4), iPad and iPhone4

Posted on Jul 18, 2012 11:16 AM

63 replies

Jan 24, 2014 11:21 AM in response to larshaeuser

I've tried all of these suggestions and nothing is working. Still saying can't unmount disk - at a dead end, any ideas?

Mar 29, 2014 10:17 AM in response to Victoria Herring

Great thread, I was about to burn my external harddrive!

Apr 14, 2014 7:44 AM in response to Drakcresure

Worked perfectly!

THANKS!

Aug 16, 2014 8:18 PM in response to niccodeamus

Thanks niccodemus! Terminal option to temporarily disable Spotlight was just what I needed; worked like a charm.

Dec 1, 2014 5:47 PM in response to desbrisay

Thank you so much! I grep'd fsck and kill the process, and my drive came back online and I was able to reinstall OS X. You Rule!!!

Dec 1, 2014 5:50 PM in response to Victoria Herring

Thank you, desbrisay !!!!!! By grep'ing fsck and killing the process, my Macbook Pro's hard drive came back online, allowing me to Format the drive and reinstall OS X.

Great Advice!!!!!!!!

quirkc

Level 1

4 points

Apr 13, 2015 11:35 PM in response to Coluch

Thank you Coluch. So simple and it worked!

19pat51

Level 1

4 points

Jun 23, 2015 7:38 AM in response to niccodeamus

Thanks for your help with this. It worked. I was able to at least erase my disk. Much appreciated.

Jul 7, 2015 3:02 AM in response to niccodeamus

Great, it helped!!!

mwereski

Level 1

0 points

Sep 10, 2015 7:58 PM in response to larshaeuser

wow this worked!!!

elooPS

Level 1

0 points

Sep 18, 2015 1:12 PM in response to Coluch

Option key heaven... thanks Coluch!! This worked first time for me, a total mac newbie!

Jan 11, 2016 12:48 AM in response to Linc Davis

Every time I have a problem with a mac, you always have the best answers. it's like the 5th time you saved my ***. I'm not even sure if you're real or not. But thank you.

Desny

Level 1

8 points

May 2, 2016 11:25 PM in response to Drakcresure

This just saved both my drive and my sanity. Thank you SO much!

Jul 13, 2016 10:49 AM in response to Victoria Herring

I have found the easiest solution ever!!!!!

1) Eject disk from desktop

2) Open Disk Utility

3) Erase!

Ps: I've tried all the top comments before but didn't worked.

DEDASS

Level 1

4 points

Aug 10, 2016 4:02 AM in response to Drakcresure

sadly I received this back 'Forced unmount of disk2 failed: at least one volume could not be unmounted'. Any advice on what to do next would be great appreciated.

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Using Disk Utility to Erase Disk-won't unmount