Fix corrupted Time Machine sparse bundles

I know that on the Internet there is an unlimited amout of articles and posts about how to solve the issue about corrupted Time Machine backups on our NASs. I have tried a lot of them when my backup has been corrupted but even following religiously their steps I didn’t get back a working backup.

This probably because Mac OS X introduced some changes during every release on how Time Machine works, making some repair process obsolete or not effective anymore. In this post I’ll describe the steps I took to fix my backup, bare in mind that it worked for me with Mac OS X 10.12.1 Sierra and I cannot guarantee that it’ll work with the previous and future versions of the OS.

Note: Before proceeding further please make a backup of your sparsebundle just in case something goes wrong and you can revert back to the original state

First become root to speed up the next steps:

sudo su -

then reset the immutable flags in your sparsebundle, replacing network_share with where your sparsebundle resides and backup_name with the name of the spasebundle to fix:

chflags -R nouchg /Volumes/<network_share>/<backup_name>.sparsebundle

Now, this step is the one missing in the most on the solutions I found and only in some posts they suggest is, in my case this was the key step of the whole recovering process.

Edit the com.apple.TimeMachine.MachineID.plist file:

vim /Volumes/<network_share>/<backup_name>.sparsbundle/com.apple.TimeMachine.MachineID.plist

set the value of the key VerificationState to 0:

<key>VerificationState</key>
<integer>0</integer>

and delete the RecoveryBackupDeclinedDate key:

<key>RecoveryBackupDeclinedDate</key>
<date>2012-09-16T01:38:43Z</date>

We are at the final stage when we first mount the sparse bundle:

hdiutil attach -nomount -noverify -noautofsck /Volumes/<network_share>/<backup_name>.sparsebundle

then looking at the output search for the Apple_HFSX entry:

/dev/diskx Apple_partition_scheme
/dev/diskXs1 Apple_partition_map
/dev/diskXs2 Apple_HFSX

and launch the filesystem recovery tool against /dev/diskXs2, note that this step will take hours to complete so it’s better to let it run overnight:

fsck_hfs -drfy /dev/diskXs2

Once the verification is complete and the filesystem is fixed unmount the sparse bundle:

hdiutil detach /dev/diskXs2

At this point the Time Machine backup should be repaired and if you run the backup it will complete without issues.

I hope this will help and if you have any questions or updates please leave a comment to this post.