Double Parity

Yesterday morning, I launched Time Machine to undo some changes I had just made to a file. But when I tried to jump back an hour, I noticed that all backups since Nov. 10 were missing. That was pretty strange since I had seen the Time Machine icon spinning in my menu bar at regular intervals all throughout the week.

Looking into the Backups.backupdb folder on my Time Machine drive, I was surprised to see two folders. One was the name of my Mac (let’s call it “doubleparity”) and held all backups prior to Nov. 10. The other was named “doubleparity 254″ and contained all backups since Nov. 10. As you’ve probably guessed, the solution to restoring my missing backups was to merge these two folders. But whenever I tried to copy or move the contents of either folder, I got a “Operation not permitted” error.

After a bit of Googling, I discovered that I had to disable Access Control Lists. Here’s a list of all the steps taken to get things working properly again:

1. Disable Time Machine

2. Backup Time Machine volume.

   Admittedly it’s rather ironic to have to backup a backup, but it’s a precaution that should be taken to keep your data safe. My Mac backs up to a ZFS filesystem on a DIY OpenSolaris server so backing up simply consists of creating a filesystem snapshot – a single command in OpenSolaris. Without ZFS, this is a considerably more complicated task.

3. Open Terminal

4. Disable ACLs

   sudo fsaclctl -p /Volumes/<Time Machine Backup>/ -d

5. Merge folder contents

   cd /Volumes/<Time Machine Backup>/Backups.backupdb/

   sudo mv doubleparity/* doubleparity\ 254/

   Here, I got an “Operation not permitted” error on the “Latest” symlink. I initially ignored it since I didn’t need the link anymore. However, I couldn’t delete the “doubleparity” folder since it wasn’t empty and all attempts to delete “Latest” gave me the same “Operation not permitted” error. I had to unmount the Time Machine volume and remount it. After that, I was able to delete the folder with no problems.

   sudo rm -rf doubleparity

   sudo mv doubleparity\ 254/ doubleparity

6. Re-enable ACLs

   sudo fsaclctl -p /Volumes/<Time Machine Backup>/ -e

7. Re-enable Time Machine

As far as I can tell, my missing backups are available and Time Machine is working normally. I still don’t know why backups suddenly started going into a second folder. If anyone out there has had a similar experience or any ideas, drop a line in comments.