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How do I force Time Machine to perform a deep traversal? I've had this happen when I needed to once before, when it took about 120 minutes to go through 500 GB and Time Machine found about 10 GB worth of data that changed, which was exactly what I wanted at the time.

Now however, I'd like to do this again, but I can't seem to do it. I've tried resetting TM by trashing com.apple.timemachine.plist, booting from my Snow Leopard startup disk (even though I'm running Mountain Lion), and probably other things that I can't think of right now (I've been spending hours on this problem so far).

When I try to perform a backup, TM wants to backup my entire drive, which is about 500 GB, when I know that not everything has changed. I can even use TM to explore folders and go backwards in time and see that many folders have not changed in a while. So, I'd like to force TM to re-index my entire drive so that it picks up only the small changes rather than decides to back up everything.

Perhaps, is there a way to purge the File System Event Store, where Time Machine goes to see what has changed recently? I assume that currently it probably lists that everything has changed, perhaps due to something I did while trying to fix this problem over the past few days.

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Deleting the .fseventsd directory on the backup drive would be one way to do it.

However in my experience there have been a few times where Time Machine did a full traversal, estimated that it would have to back up the entire drive, and then proceeded to check everything but only back up files that were different. For example, this happened after upgrading from 10.7 to 10.8. The size of the new backup was much less than it first estimated.

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Is the "backup drive" the source (the thing I am backing up) or the destination (the place where I am placing all my backups)? Also, I suspect that when TM says it's backing up 500 GB, it's the truth, because it's deleting all my old backups. I'd rather not take the risk of having it delete all my backups, anyway. –  Gary Oct 21 '12 at 3:35
    
I meant the destination, but in theory you could delete either one. It's just a bit safer to play with the one you aren't booted from. It is unfortunate that it wants to make room for 500GB, whether it actually needs 500GB or not. You can try removing the directory - I'm just not positive a deep traversal is going to help. –  gabedwrds Oct 21 '12 at 3:39

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