Currently Being ModeratedJul 18, 2012 11:23 AM (in response to Victoria Herring)
Are you booted from the drive you are trying erase?
Currently Being ModeratedJul 18, 2012 11:53 AM (in response to Victoria Herring)
Boot into Recovery (command-R at startup) and erase the volume.
Currently Being ModeratedJul 18, 2012 12:03 PM (in response to Linc Davis)
No i am not booted into that drive but the idea of the Recovery drive to wipe it sounds good = thanks much.
Currently Being ModeratedJul 18, 2012 12:53 PM (in response to Victoria Herring)
Just reporting back that I rebooted into Recovery [held Option key down at startup and chose the Recovery HD] and it did what I needed...thanks much
Currently Being ModeratedSep 23, 2012 7:58 AM (in response to Victoria Herring)
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)
Currently Being ModeratedJan 8, 2013 7:14 AM (in response to niccodeamus)
Thanks that terminal advice was spot on. I even set a one-on-one session and we could not figure it out. Thanks!
Currently Being ModeratedMar 24, 2013 8:25 AM (in response to niccodeamus)
Made an account to say that was just what I needed to assist with an external drive I was trying to erase. Thanks niccodeamus!
Currently Being ModeratedJun 30, 2013 7:11 AM (in response to niccodeamus)
Logged into my old account to thank niccodeamus, big help! Thought I was going to have to buy a new external!
Currently Being ModeratedJul 10, 2013 8:43 AM (in response to Victoria Herring)
I tried the terminal option but I still got this error
Partition failed with the error:
Couldn’t unmount disk.
Is my only option to "Boot into Recovery (command-R at startup) and erase the volume." ?
Currently Being ModeratedSep 11, 2013 9:52 AM (in response to fineartist99)
Had a similar issue, The drive would not unmount in disc utility to be erased, disk warrior could not even see it.
I used the sudo command that niccodeamus suggested, I also forced quit the fsck_hfs process, my drive then began to erase without issue
Currently Being ModeratedOct 3, 2013 9:52 AM (in response to Victoria Herring)
Thanks for the above info!
I had a similar problem, Disk Utility would not erase and reformat my external disc and complained about being unable to erase the external disc.
I tried disabling Spotlight as described above, but that didn't fix the problem.
I then searched for an fsck process:
ps -ax | grep fsck
and then killed that process:
sudo kill <process number>
Problem solved! Disk Utility then successfully erased and reformatted the external drive!
Many thanks for the clues that led me to this solution!
Currently Being ModeratedNov 19, 2013 9:11 AM (in response to desbrisay)
Currently Being ModeratedDec 27, 2013 10:51 PM (in response to taramaple)
I had similar problem, can't unmount easily.
Ending up connecting the disk as a target disk (holding T key on startup) connected to another Mac.
Then using terminal, used the following commands to force unmount disk and erase the disk after.
To check for the exact name of the disk:
sudo diskutil list
(you will see the list of drives/partitions, take note of which one is the one you are trying to unmount/format, should be something like /dev/disk<number>)
Then to force unmount disk:
sudo diskutil unmountDisk force /dev/disk<number>
You should get a response to the success or failure to the unmount command.
Then if you want to format force format the disk:
sudo diskutil erasedisk JHFS+ Untitled /dev/disk<number>