studio_

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

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  • by studio_,

    studio_ studio_ Jan 21, 2014 3:33 PM in response to Kappy
    Level 1 (2 points)
    Jan 21, 2014 3:33 PM in response to Kappy

    Dang it, I meant to click "this solved my question" sorry :/

  • by Kappy,

    Kappy Kappy Jan 21, 2014 7:14 PM in response to studio_
    Level 10 (271,406 points)
    Desktops
    Jan 21, 2014 7:14 PM in response to studio_

    Try again.

  • by ragarose,

    ragarose ragarose Mar 29, 2014 7:48 PM in response to studio_
    Level 1 (0 points)
    Mar 29, 2014 7:48 PM in response to studio_

    I am running Mavericks 10.9.2 and am having the same problem, but am unable to fix it with the help suggested by Kappy and Dr.Mac.  Specifically, I have a WD Passport external hard drive (formatted FAT) with a single partition that doesn't show up in Finder when I plug in the HD.  I can find the disk in Disk Utility, but cannot repair it, eject it, or unmount it when I try to erase and/or re-partition the disk. 

     

    Things I have tried: unplugging the HD and plugging back in, restarting my computer, restarting and holding command+r to enter disk utility, entering Terminal and typing "diskutil unmountDisk force disk1", disabling Spotlight in Terminal ("sudo mdutil -a -i off") then trying to force disk unmounting (above command and "sudo diskutil unmountDisk force disk1")

     

    ....and still the disk will not unmount!  What should I do?

     

    BTW, here is the response in Terminal after the command diskutil list:

    /dev/disk0

       #:                       TYPE NAME                    SIZE       IDENTIFIER

       0:      GUID_partition_scheme                        *500.1 GB   disk0

       1:                        EFI EFI                     209.7 MB   disk0s1

       2:                  Apple_HFS Macintosh HD            499.2 GB   disk0s2

       3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

    /dev/disk1

       #:                       TYPE NAME                    SIZE       IDENTIFIER

       0:     FDisk_partition_scheme                        *1.0 TB     disk1

       1:                 DOS_FAT_32 BEAVER                  1.0 TB     disk1s1


  • by Walt D in LV,

    Walt D in LV Walt D in LV May 16, 2014 8:32 AM in response to ragarose
    Level 1 (14 points)
    May 16, 2014 8:32 AM in response to ragarose

    ragarose, did you ever get an answer to your problem?

     

    I am having the same problem as yours, that is, slightly different than the original poster.

  • by satxusa,

    satxusa satxusa May 24, 2014 3:21 AM in response to Walt D in LV
    Level 1 (0 points)
    May 24, 2014 3:21 AM in response to Walt D in LV

    I had the same error message when trying to reformat and reinstall Mavericks, but was unable to follow all the steps outlined, but did restart the computer and simply turned off Time Machine, then again restarted and was able to erase the hard drive without the error.

  • by Mark Bishop,

    Mark Bishop Mark Bishop May 29, 2014 9:33 AM in response to Kappy
    Level 1 (85 points)
    May 29, 2014 9:33 AM in response to Kappy

    I'm having the same problem. My WD external disk won't unmount. I tried the Terminal command you suggested and got this response:

     

    Forced unmount of disk1 failed: at least one volume could not be unmounted

     

    Any other options?

  • by Mini-Mac,

    Mini-Mac Mini-Mac May 29, 2014 9:51 AM in response to satxusa
    Level 3 (811 points)
    May 29, 2014 9:51 AM in response to satxusa

    Just had the same issue (yesterday) with USB drive (USB3.0) would not un-mount that had a (2nd) Time Machine backup on it.

     

    I actually thought the disk died, because I just tuned off the power  to the disk (I know it's not a good idea to power down without un-mounting).  When I powered the disk back up the drive would not mount even after a restart.  I took the disk out of the Voyager S3 and put it into a external enclosure and bam the disk was working again.  I repaired the disk (using DU Repair Disk, no errors) and put it back into the Voyager S3 and the disk is fine now.

     

    So I have NO idea what happen other than a possible Maverick bug of some sort.

  • by Exactive,

    Exactive Exactive Jun 3, 2014 9:23 AM in response to Mini-Mac
    Level 1 (0 points)
    Jun 3, 2014 9:23 AM in response to Mini-Mac

    Had the exact same problem, disk would not unmount no matter what I did. I solved the problem by taking the external disk to a windows box and cleaning it using the diskpart command line tool and the clean command. Then plugged it back into my mac and erased it. It  All works now...

  • by tjyoung82,

    tjyoung82 tjyoung82 Jun 25, 2014 8:48 PM in response to Kappy
    Level 1 (10 points)
    Jun 25, 2014 8:48 PM in response to Kappy

    Thank you so much Kappy!!!  That was huge...it worked, and within seconds at that!  My external hard drive is back!  And I didn't even have to restore it!

     

    A million thanks...

  • by Ajay Joon,

    Ajay Joon Ajay Joon Sep 16, 2014 8:41 PM in response to Kappy
    Level 1 (0 points)
    Sep 16, 2014 8:41 PM in response to Kappy

    Thanks Kappy. This solved my problem ..:)

  • by Rico.fm,

    Rico.fm Rico.fm Nov 17, 2014 12:40 PM in response to Mark Bishop
    Level 1 (4 points)
    Nov 17, 2014 12:40 PM in response to Mark Bishop

    Ok, so same problem - found this thread, etc.

     

    Tried 2 different Imac's, Macbook and nothing. It won't unmount. I believe it has to do with the fact that TimeMachine backups were on this external WD 1TB drive.

     

    So, used an ASUS Laptop with WIN 8.1 and ran the following:

    http://wdc.custhelp.com/app/answers/detail/a_id/3865/~/how-to-partition-and-form at-a-wd-drive-on-windows-(8,-7,-vista,-xp)-and-mac-osx

     

    I was able to delete the drive and then reformat with MAC.

     

    Hope this helps others.

  • by pdanielsen,

    pdanielsen pdanielsen Nov 25, 2014 6:14 PM in response to Rico.fm
    Level 1 (0 points)
    Nov 25, 2014 6:14 PM in response to Rico.fm

    I had this problem on 10.10.1 with an external Firewire drive when trying to erase it with DiskUtility.  No change after disabling Spotlight.  I had my GoPro Hero3 also mounted as another drive.  I ejected it and then DiskUtility was able to erase the Firewire drive. 

     

    Hope this is helpful to someone else who ends up here.

  • by BBQ100,

    BBQ100 BBQ100 Nov 28, 2014 3:04 PM in response to Kappy
    Level 1 (0 points)
    Nov 28, 2014 3:04 PM in response to Kappy

    This was fabulous - helped me reformat an external hard drive to mac - wasn't letting me format until I turned off spotlight. it was trying to index the new hard drive. THANK YOU!

  • by seretuaccidente,

    seretuaccidente seretuaccidente Jan 12, 2015 10:40 AM in response to Kappy
    Level 1 (0 points)
    Jan 12, 2015 10:40 AM in response to Kappy

    Hi Kappy, similar problem here

     

    I used an external hard drive to install Yosemite (creating a single partition) and boot my computer from there, as I had a problem with my internal hard drive.

     

    Now everything is working fine with my computer and I wanted to format the external hard drive. But it happens that when I try to erase the partition (Mac OS Extended or create new ones with disk utility I get the message "couldn't open disk" or "couldn't unmount disk". I've tried to verify/repair disk and, after a couple error messages ("This disk needs to be repaired" and "Disk utility can't repair disk, erase it") I'm in the starting point.

     

    The "stop spotlight" thing didn't change anything, neither the "sudo diskutil unmountDisk force disk1" option

     

    If I enter "diskutil list" in Terminal, what I get in response is:

       #:                   TYPE NAME                SIZE   IDENTIFIER
       0:  GUID_partition_scheme                    *121.3 GB   disk0
       1:                    EFI EFI                 209.7 MB   disk0s1
       2:      Apple_CoreStorage                     120.5 GB   disk0s2
       3:             Apple_Boot Recovery HD         650.0 MB   disk0s3

    /dev/disk1

       #:                   TYPE NAME                SIZE   IDENTIFIER
       0:              Apple_HFS Yosemite HD        *120.1 GB   disk1
                                 Logical Volume on disk0s2
                                 A8CE2C6C-716E-4527-B949-F8DE1CA75BEF
                                 Unencrypted

    /dev/disk2

       #:                   TYPE NAME                SIZE   IDENTIFIER
       0:  GUID_partition_scheme                    *4.0 TB disk2
       1:                    EFI EFI                 209.7 MB   disk2s1
       2:              Apple_HFS fuco                4.0 TB disk2s2
       3:             Apple_Boot Recovery HD         650.0 MB   disk2s3

     

    Don't really know what to try now.

  • by bluesimage,

    bluesimage bluesimage Feb 7, 2015 3:15 PM in response to studio_
    Level 1 (0 points)
    Feb 7, 2015 3:15 PM in response to studio_

    I was having the exact same problem in Yosemite and I discovered a simple solution without any Recovery HD or terminal stuff.  It was just a Time Machine issue.

     

    In my case, I was trying to erase an external HD that was different from the last one I used with Time Machine. The easy solution:

    1. Open Time Machine Preferences

    2. Turn off Time Machine if it is on

    3. Select the available external HD that you want to erase

    4. Click "Use Disk"

    5. If you get another dialog box, chose the "Replace. . ." option to get the previous disk out of the way

    6. Now you should be able to erase your external HD

    7. Reset Time Machine however you want.

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