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Disk Utility cannot unmount disk

I am trying to reinstall snow lepord on a macbook pro. When I go to repartition the drive it fails and tells me that it cannot unmount the disk. Any ideas?

MacBook Pro, Mac OS X (10.6.7)

Posted on Sep 23, 2011 12:51 PM

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64 replies

Jul 12, 2017 1:20 AM in response to hoosier

Since this is still the top hit for the question...

I know this is a major necropost, but just in case someone stumbles across this thread, here is the solution. I wish I had found the answer *before* I threw away those couple of "dead" drives, lol.


Some damaged disks do not show up with Disk Utility and DiskWarrior, and may hang and crash such repair utilities. Yet, there is a trick to repair such broken disks using Disk Arbitrator.


1. Open Disk Arbitrator and select "Activated - Block mounts." This prevents the damaged disk from crashing the repair utilities and allows such disks to be displayed by these utilities.


2. Connect the damaged disk.


3. Open Disk Utility or DiskWarrior. The damaged disk should show now and it should not crash the repair utility.


4. Deactivate Disk Arbitrator (uncheck the Activated box). This allows the repair utility to handle the damaged disk properly (mounting it once repaired).


5. Run Disk Utility or DiskWarrior.


Then, the utility should repair the disk, or at least, mount a Preview disk (DiskWarrior), allowing you to inspect and even copy or backup some files or the full disk, reformat it and restore it.


Here is where to get it:

Releases · aburgh/Disk-Arbitrator · GitHub

Jul 19, 2017 9:01 PM in response to hoosier

Hi hoosier,

The primary cause of facing disk utility could not unmount hard drive is the modification of the boot drive or it is being used by some other process or application.

If the internal Mac hard drive is causing this problem due to macOS, recovery exists as partition and unable to change or unmount the Mac HD, then you should choose the network based drive or any powerful external hard drive.

Sep 23, 2011 1:36 PM in response to hoosier

Not without losing everything. Well, then, let's try something different.


Boot into Single-user Mode:


After startup is completed you will be in command line mode and should see a prompt with a cursor positioned after it. At the prompt enter the following then press RETURN:


/sbin/fsck -fy


If you receive a message that says "***** FILE SYSTEM WAS MODIFIED *****" then re-run the command until you receive a message that says "** The volume (name_of_volume) appears to be OK." If you re-run the command more than seven times and do not get the OK message, then the drive cannot be repaired this way. If you were successful then enter:


reboot


and press RETURN to restart the computer.

Disk Utility cannot unmount disk

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