Previous 1 2 Next 16 Replies Latest reply: May 1, 2014 5:53 AM by Karen.L.P.
elliswicks Level 1 (0 points)

Hi guys,


I've been using my Seagate Portable Media 500GB external hard drive for Time Machine on Mountain Lion.


Last week, Time Machine's backup failed, with the message "Unable to complete backup. An error occurred while creating the backup folder."


Using Disk Utility, I verified the disk which asked me to repair it. On trying to repair it, I received the message "Couldn't unmount disk". I received this message also when trying to Erase or Partition the drive and I don't know how to take it further.


The drive is still visible in Finder and I can still access its contents.


I've also tried using a new power cable for the drive and I'm having the same results.


Any advice would be great!



iMac (21.5-inch Mid 2011), OS X Mountain Lion (10.8.2)
  • Joe Gramm Level 5 (6,340 points)

    When this happens to me I boot into the Recovery HD to repair the disk. Restart the computer and hold the Command+R keys until you see the Apple symbol. Once in Recovery HD, select Disk Utility and Repair the Disk.

  • elliswicks Level 1 (0 points)

    That seems to have solved it for now! Thanks! Does it do this often?

  • Joe Gramm Level 5 (6,340 points)

    I have a 1 TB Iomega drive that I need to repair every so often. It's okay as long as I can resume the back ups without having to start a "New" backup. A new backup then becomes aggrevating to have to do.

  • Joe Gramm Level 5 (6,340 points)

    Just an update:

      If you run into trouble after repairing the Disk with TM trying to do a full new backup, try James Pond's method of doing a Total Reset. This has got TM back doing incremental back ups vs a new backup.

  • elliswicks Level 1 (0 points)

    Hi Joe, I've tried both of these and I seem to still be having the same problem. After the Time Machine has done a few backups and seems fine, it "corrupts" and has to be completely wiped and start all over! I've tried the total reset and fully repairing/erasing the drive, to no avail.


    This is becoming annoying as I have to do a full erase and full Time Machine backup of the drive every time it does this.


    Any more suggestions?

  • Joe Gramm Level 5 (6,340 points)

    Do you have any other external drives plugged into (daisy chained) your Time Machine disk. The reason I ask is I've found out what my problem is when TM says it's not able to do a backup. I have another external drive plugged into my TM disk. Whenever I unmount the second drive, my next TM backup will not complete. I boot into the Recovery HD/Repair Disk and then TM will work perfectly until I unmount the second drive the next time.


    I assume you have the drive formatted to HFS+.  Below from Seagate:


    * The drive must be reformatted to HFS+ in order to use backup software for Mac or Time Machine software

  • elliswicks Level 1 (0 points)

    No I have no other daisy chained drives so this can't be the issue.


    When I go to Disk Utility, I am only given the option to Erase my drive and change it to formats such as: Mac OS....,MS DOS, EXFAT etc.....there is no HFS+ format?


    How would I do this?

  • Joe Gramm Level 5 (6,340 points)

    Don't know why they state it like that. I think it should be formatted  Mac OS Extended (Journaled)

  • elliswicks Level 1 (0 points)

    It is

  • elliswicks Level 1 (0 points)

    Any ideas on what I can do now?

  • elliswicks Level 1 (0 points)

    Any ideas at all for what I could do now?

  • brittney.vlam Level 1 (0 points)

    I also could not unmount my external harddrive. I tired everything and this was my last chance and it worked! Super excited to have 1TB external back and fully functional again.

  • Galaxy User Level 1 (0 points)

    Hi elliswicks,



    Please follow this step before atempting Joe Gramm's "boot into recovery" method.


    1) Keep your external hard drive plugged in.


    2) Restart your computer.


    3) Go to Disk Utility and eject the drive.


    You should have no problems carrying out Step 3. If this fails, you'll have to rely on Joe Gramm's advanced method.


    Hope you (and anybody else) have benefited from this simpler method! Don't forget to like or put "This solved my question" or "This helped me"!


    Good luck!

    from Galaxy User

  • Joe Gramm Level 5 (6,340 points)

    Galaxy User wrote:


    Hi elliswicks,


    Please follow this step before atempting Joe Gramm's "boot into recovery" method.


    Keep in mind you are replying to a post that is a year old and likely not an issue anymore.

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