Problems with Time Machine endlessly preparing

We use Time Machine with a network disk connected via AirPort Extreme for backup in our household (writeup), and it’s generally a great solution. However recently my wife’s laptop had got stuck in an endless “preparing backup” situation. There didn’t seem to be any significant details in the error log, and when I ran a Disk Utility on the Sparse Bundle associated with her laptop nothing came up. My laptop was backing up over the network from the same drive, so I was fairly sure everything was working with the setup.

After a fair bit of googling I came up with Patty Patty’s solution (scroll down to Patty Patty’s post on Jun 1, 2008 12:45 PM) on the Apple discussion boards which I’ll rekey here for convenience:

  • Turn Time Machine off
  • Trash the com.apple.TimeMachine.plist in /Library/Preferences
  • Restart

I then turned Time Machine back on, and the next backup ran fine. Bear in mind that although this worked for me, any issue you have may be different and your mileage may vary. Patty Patty (gender unknown) went on to suggest the following, although I didn’t need to go this far:

  • Full Spotlight reindex of the Macintosh HD
  • Added a bunch of folders to the “Do Not Backup” list in Time Machine
  • Turn Time Machine on

The one difference I could spot between my wife’s setup with her laptop (which had the issues) and mine (which didn’t), is that her network connection is almost solely wifi and mine is often ethernet. Some other reports I read suggested that when connections are interrupted over wifi it can screw with Time Machine. Other reports I read suggest that Apple may still be working on this in upcoming releases… but given Apple’s usual level of transparency and predictability I think we should all take that one with a pinch of salt.

Hope this helps someone.

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