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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

Sep 23, 2011 2:13 PM in response to hoosier

Drive Preparation


1. Boot from your OS X Installer Disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu.


2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Note the SMART status of the drive in DU's status area. If it does not say "Verified" then the drive is failing or has failed and will need replacing. SMART info will not be reported on external drives. Otherwise, click on the Partition tab in the DU main window.


3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, set the partition scheme to GUID then click on the OK button. Click on the Partition button and wait until the process has completed.


4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.


5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.


6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.

Sep 23, 2011 3:14 PM in response to Kappy

@Kappy you can not "fix" mean write something to drive without mount it w

check yourself - boot single and read some last 2-3 strings - there it is


@hoosler your mac should be able to boot in target mode

read here instructions http://www.techrepublic.com/blog/helpdesk/boot-a-sick-mac-into-target-disk-mode- for-troubleshooting/293

try to repair/repartition target drive from other mac

also read this: http://support.apple.com/kb/ht1661

Sep 23, 2011 3:39 PM in response to Kappy

its simple - just try it and you'll see.

look:

"

If fsck found issues and has altered, repaired, or fixed anything, it will display this message:

***** FILE SYSTEM WAS MODIFIED *****

"

file system can not be modified while r-only mounted


looks like error or not exact description.



@hoosier also you can give a try with a Disc Warrior or Drive Genius

Jan 22, 2012 8:34 AM in response to hoosier

The problem I was having was with a Toshiba 500GB external USB 2.0 drive. The symptom was that the Mac OS X Disk Utility could see the drive but trying to format it would hang indefinitely at "Unmounting Drive".


I formatted the disk with the built in disk format and partitioning tools in Windows 7. Then I could mount and unmount on the Mac OS X Disk Utility. Maybe using utilities in Linux would also work. After this I was able to format the disk in Mac OS X and use the drive for time machine.


How my problem started: Hooking up the drive to the WNDR3800 router seemed to mess it up and my Mac coul no longer reaad the disk correctly. Foratting it in a Windows env was the only way I could get it to work again on my Mac.

Disk Utility cannot unmount disk

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