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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

Top-ranking reply

niccodeamus

Level 1

6 points

Posted on Sep 23, 2012 7:58 AM

I realise that you have solved this problem, but I have solved a similar issue differently.

It appeared that the external drive would not unmount because some activity was using it. fsck_hfs process was working away as shown by activity monitor. It seems that Spotlight was struggling with a the failed drive and would not let it go so the unmount and erase could not occur.

This was solved by disabling Spotlight (terminal: sudo mdutil -a -i off) temporarily. After disabling Spotlight, Disk Utility performed its job and my corrupted drive was restored to use.

(Spotlight is turned back on with: sudo mdutil -a -i on)

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63 replies

PaoloT.

Level 1

11 points

Nov 3, 2016 2:38 AM in response to Victoria Herring

I solved this issue in a slightly different way.

1. An external Time Machine backup drive refuses to work, unmount, be reinitialized from Disk Utility.

2. Open Activity Monitor, and select the fsck_hfs process.

3. In Disk Utility, start initilizing the external drive. DU will say that it is trying to unmount the drive.

4. Immediately quit fsck_hfs from Activity Monitor.

5. With the external drive left free from fsck_hfs, DU will reinitialize it.

Paolo

Bayonjay

Level 1

4 points

May 22, 2017 10:02 AM in response to Victoria Herring

Hi All,

Tried all the terminal and process solutions, but was still having trouble... then I realized that the terminal was mentioning the WD apps (external drive) in the indexing shut down process. I unmounted/forcibly quit the WD Apps and it finally worked.

Just thought it might be helpful for anyone with those "smart drives" that automatically install odd drivers/apps. The drive can't be running anything when you try to unmount it and erase it. If you're worried about erasing those apps, copy the files to your onboard drive.

Jul 2, 2017 12:58 PM in response to Victoria Herring

This is an old thread, so I don't know if anyone from previous will be following it, however...

I had the same issue with a brand new WD 4TB My Book. At one point, it had completely screwed up the drive and I couldn't do anything with it at all. (It was an hour old.) Just before I threw in the towel, I decided to try the software that came with the drive. And voila! It worked! This is after trying all the other suggestions that I had read on here. Being fairly comfortable with trying other options, I did.

oakharoh

Level 1

12 points

Aug 7, 2017 2:05 AM in response to larshaeuser

Can you please explain this process for a novice? I just purchased a (used) Air that was only configured to start on OS X Utilities.

I attempted to reinstall os x (reinstall is Yosemite) however, never seem to make it beyond entering Apple id.

When this failed, I attempted a repair and erase. An error message "couldn't unmount disk" pops up.

How do I get past without an install disk? I have downloaded os x 10.5 on a USB.

Thank you!

Sep 16, 2017 12:36 PM in response to Victoria Herring

For those who had this problem with WD disk:

Install the "WD drive utilities" software that comes along with disk. After you install and open that software, choose "drive erase" and do the erasing there. Then you'll be fine.