3 Replies Latest reply: Apr 19, 2013 9:48 AM by putnik
jnbecker Level 1 Level 1 (0 points)

I have a MacBook Pro and use Time Machine to back-up to a 500 GB Western Digital external hard drive. The solution's worked fine for years until the other day when I got a message saying the back-up couldn't be completed because the hard drive is set to read-only. Each time it goes to back-up I now get that same message. I have not knowingly changed any settings on the hard drive. When I check the drive it shows as being almost full, but I thought Time Machine automatically removed the oldest back-up when it needs more space for the next one. How can I reset the disk to read/write? Do I have another problem?

MacBook Pro, OS X Mountain Lion (10.8.3)
  • 1. Re: Suddenly Can't Back up to External Hard Disk
    putnik Level 3 Level 3 (690 points)

    First I would do some checks on the disk itself. Start by running Repair disk from Disk Utility in your Utilities folder.  Check the SMART status if you can too.  If all seems to be ok then can you actually see what is on  the disk in Finder?


    Pondini is the expert on Time Machine and his diagnostics are a good place to start troubleshooting TM generally.



  • 2. Re: Suddenly Can't Back up to External Hard Disk
    jnbecker Level 1 Level 1 (0 points)

    Thanks for the guidance. When I ran Disk Repair it took a while to run and, in the end, it said it found too many problems to repair the disk. It said all the data is still there, that I should back it up, reformat it, restore the back-up then hopefully I could start using Time Machine again. The problem I have with that is that I don't have anything to back the external hard disk up to. All that's on it are Time Machine back-ups. Since I can't access them now anyway, is there any problem with just going ahead and reformatting the disk (not doing the back-up) and then just starting to use it with Time Machine again once its reformatted? I know that, during the time until I do the first back-up with the newly reformatted disk, I will be exposed and without any back-up, but shouldn't the disk work fine again once it's reformatted? Or is there a chance it's too corrupt to work even after being reformatted? Other suggestions?

  • 3. Re: Suddenly Can't Back up to External Hard Disk
    putnik Level 3 Level 3 (690 points)

    I would think the disk is failing and although it may move data to good segments and look ok for a while, eventually something critical will fail and you will lose everything.  Maybe I am being pessimistic and you could try to check the SMART status and use more powerful tools than Disk Utility, such as Disk Warrior.


    I would buy a replacement disk and start a new backup set, either using Time Machine or make a bootable clone using Carbon Copy Cloner (CCC) or SuperDuper etc.  The clone has some advantages in that you can conduct more tests from outside your system, do erase/installs etc.