How to fix a Corrupted Time Machine Backup

The other day time machine decided to stop working for me and kept giving me errors about mounting the backup image. After firing up Console.app I found that the sparsebundle which time machine stores the backup data in was corrupted. This is a bad thing since if I couldn’t find a way to fix the image all my backups for the last 6 months would be lost :(.

My first step on the road to fixing the problem was to open the bundle with “Disk Utility” and see if repair disk would work. To do this you need to drag the back image (the .sparsebundle) and drop it on disk utility. Then you can select the image and press “Repair Disk”. Usually if if you have some disk corruption this would fix it, but not for me.

After working for a couple minutes Disk Util would fail at repairing the disk since it found an “Invalid Sibling Link”. It seems the disk was corrupted and the disk repair utility decided it wasn’t going to repair it. Worried that my backups were gone for good I did some Googling and found that this problem isn’t totally uncommon. It seems that Disk Utility is just fairly bad at repairing disks and that using the “real” disk repair utility fsck_hfs might actually fix the problem.

Of course there’s one problem fsck_hfs has to be used directly on a block device not a “sparsebundle” disk image. Not only that but the volume you run the util on cannot be mounted and OS X always tries to mount the image when you click on it. The solution? Use the command line tool hdiutil to “attach” but not “mount” the image. This makes OS X create a /dev/ device for the sparse bundle but doesn’t actually mount the filesystem.

So combining hdiutil and fsck_hfs we might have a way to fix the disk image. Note: Make sure you turn off Time Machine in the System Preferences panel. We don’t want Time Machine trying to mount our image and back up to it until we’re done making all the repairs.

First I ran hdiutil:

hdiutil attach -nomount -readwrite Bhaal_0011247e3338.sparsebundle

After a minute or two of thinking we had success:

/dev/disk1              Apple_partition_scheme
/dev/disk1s1            Apple_partition_map
/dev/disk1s2            Apple_HFSX

The next step was run fsck_hfs on the main volume.

fsck_hfs -rf /dev/disk1s2

-f is required to force a check since this is a journaled file system. I also used -r to have it rebuild the filesystem catalog for the “invalid sibling link” this is required (thanks Dan). At this point I went out for breakfast since I was running a disk repair utility over my wireless internet to my Linux SAMBA server. After coming back from breakfast we had success!

** /dev/rdisk1s2
** Checking Journaled HFS Plus volume.
** Detected a case-sensitive catalog.
** Checking Extents Overflow file.
** Checking Catalog file.
** Rebuilding Catalog B-tree.
** Rechecking volume.
** Checking Journaled HFS Plus volume.
** Detected a case-sensitive catalog.
** Checking Extents Overflow file.
** Checking Catalog file.
   Incorrect number of thread records
(4, 13716)
** Checking multi-linked files.
** Checking Catalog hierarchy.
   Invalid directory item count
   (It should be 0 instead of 1)
   Invalid directory item count
   (It should be 3 instead of 4)
   Incorrect folder count in a directory (id = 3795486)
   (It should be 0 instead of 1)
** Checking Extended Attributes file.
** Checking multi-linked directories.
** Checking volume bitmap.
** Checking volume information.
   Invalid volume free block count
   (It should be 37267681 instead of 37310834)
   Volume Header needs minor repair
(2, 0)
** Repairing volume.
** Rechecking volume.
** Checking Journaled HFS Plus volume.
** Detected a case-sensitive catalog.
** Checking Extents Overflow file.
** Checking Catalog file.
** Checking multi-linked files.
** Checking Catalog hierarchy.
** Checking Extended Attributes file.
** Checking multi-linked directories.
** Checking volume bitmap.
** Checking volume information.
** The volume Backup of Bhaal was repaired successfully.

111 thoughts on “How to fix a Corrupted Time Machine Backup

  1. hi,
    first of all best wishes for 2012,
    the 1st of jan i decided to re-install my mac, after reinstall impossible to access the backup … 870gb of data lost,
    thanks to you I recovered everything after 40hours ..!
    merci – merci – merci !!!!!!!

  2. Hi,

    When I issue the “hdiutil attach -nomount -readwrite” command I get his error,

    hdiutil: attach failed – Read-only file system

    I have even tried the command as root and get the same error.

    My TM sparse bundle is on a Synology DiskStation and I have R/W access to that location so I’m baffled why I get the error.

    Any thoughts appreciated.

  3. Ok, Im a little new here and would like some assistance.
    i tried reading thru the past posts but its confusing for me.
    Im having trouble with my TM and TC. It keeps saying “disk cannot be mounted”. I bit the bullet and reformat my TC! but it still says “disk cannot be mounted”..!! I don’t know what to do next..? please assist.. thank you in advance.

    Aj

  4. this is what am getting

    Executing fsck_hfs (version diskdev_cmds-540.1~34).
    ** Checking Journaled HFS Plus volume.
    ** Checking extents overflow file.
    ** Checking catalog file.
    ** Rebuilding catalog B-tree. ** The volume could not be repaired.

  5. I tried the first step, but i keep getting “hdiutil: attach failed – No such file or directory” I’m probably forgetting something, but not sure what

  6. I wonder if “Bhaal_0011247e3338″ is the name of your disk because Terminal replies: hdiutil: attach raided – No such file or directory
    ?
    Thanks for a reply.

  7. Yes, “Bhaal_0011247e3338? was the name of my sparsebundle file. Substitute the name of your disk/sparsebundle instead of mine.

  8. I need help. I have my time machine backed up on a Windows 7 network computer. I can not get past the first step. I am running the following command: hdiutil attach -nomount -readwrite smb://my-desktop/TimeMachine/TimeMachine.sparsebundle

    where my-desktop is the computer name of the Windows 7 machine. The error I get is: hdiutil: attach failed – not recognized

    Can anyone help?

  9. Hi!
    I Encountered some problem with my hd where I stored my time machines files since November 20 2012… (Ouch!)
    After I did “Repair Disk” mi iMac 2011 is unable to read my hd again to store the new files of the Time Machine. TM is also unable to see the HD.
    I can practically only read the file but the HD is corrupted, because Disk Utility can’t repair the disk again.
    What can I do to repair the integrity of the disk?
    I hope tris thread is still active..

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