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Disk Erase failed with the error: Couldn’t unmount disk. Running Mavericks

I am running Mavericks OX 10.9.1 and am trying to erase an external hard drive that has been partioned. I keep coming up with the error message "Disk Erase failed with the error: Couldn’t unmount disk." Any suggestions?

iMac, OS X Mavericks (10.9.1)

Posted on Jan 21, 2014 1:45 PM

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49 replies

Mar 29, 2017 8:46 PM in response to studio_

Hi, I've just solved the same problem successful 100%.

Step 1: Right after turn macbook on, press "Option-Command-P-R" to Reset NVRAM (See more Startup key combinations for Mac - Apple Support)

Step 2: Fix with USB Boot Drive (find how to create USB Boot https://www.youtube.com/watch?v=W7bPfNREVMU)

Step 3: Select Hardrive you want to fix + select First aid tab + "Verify" and "Repair"

Step 4: Press "Command + R" to reinstall normally.

Be successful!

Nov 8, 2017 12:29 PM in response to studio_

OK, this is 3 years later than the OP, but I have a different solution to what appeared to be the same problem.


NB: I am not 'happy' with doing anything involving Console or Terminal: it is too easy to do the wrong thing which would be a disaster!


I have an old external HD which had been used as a back-up about 4 years ago. I wanted to clear all the data, to leave it available for reuse by me or others. Using the Disk Utility to do a secure erase was not possible (even the simple one-pass of zeroes) and the same message was displayed as others have reported.


After reading the advice here and deciding that I didn't trust myself to do it properly, I went back to the HD, and sent all the content to Trash. This involved entering my admin password, but was successful. (Yes, I know that means it is still there!)


I was then able to use the Disk Utility to Erase by one-pass with zeroes, although I imagine all other lengthier options would have worked equally well.


I hope that this very simple work-round will be useful for some other non-tech users, and I will be happy for any of the more tech-savvy to tell me of any drawbacks to this procedure.

Jan 21, 2014 2:17 PM in response to studio_

There must be something on the drive that has a connection to the internal drive, I think. Try booting from the Recovery HD:


Boot to the Recovery HD:


Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the arrow button below the icon.


Select Disk Utility from the list and click on the Continue button. See if this lets you erase the drive.

Jan 21, 2014 2:26 PM in response to studio_

To list all the drives and their accompanying partitions from the Terminal, type the following command:


diskutil list


This will give you a listing out the drives, their volume names, the size of the drive and partitions, their partition types, and their identifier location. Paste the disk drives listing into a reply to this message.




Jan 21, 2014 3:17 PM in response to Kappy

sorry, I should clarify. I was able to eject the external HD, but after waiting a few minutes and reconnecting it, I was still not able to erase the external hard drive.


I also tried to erase the drive after a simple restart of the computer. That did not work.


When I restarted the computer with command + r at the chime, the menu came up, but did not have the option of "Recovery HD".


I can try again and tell you what my options are if that will help...

Jan 21, 2014 3:21 PM in response to Dr.Mac.

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *2.0 TB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS OSX 869.3 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

4: Apple_HFS TAGP 1.1 TB disk0s4

5: Apple_HFS Scratch 49.8 GB disk0s5

/dev/disk1

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk1

1: EFI EFI 209.7 MB disk1s1

2: Apple_HFS Production iMac Clone 250.0 GB disk1s2

3: Apple_HFS Production iMac Time... 749.7 GB disk1s3

Jan 21, 2014 3:21 PM in response to studio_

Here's a suggestion you might try:


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)


This is from a 2012 discussion re: this problem. It helped some users, so give it a go.

Disk Erase failed with the error: Couldn’t unmount disk. Running Mavericks

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