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Time Machine is doing very large backups

1015 Views 15 Replies Latest reply: Feb 17, 2013 10:08 AM by Linc Davis RSS
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roolo Calculating status...
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Feb 14, 2013 12:04 PM

Background: I bought new drive for Time Machine backup. First backup took about an hour and backed up about 80 GB (let's considered as good behaviour). Second backup was supposed to be above 70 GB (bad behaviour, bad) which could not really be the amount of data actually changed for the while between backups.

When i try manually run tmutil compare in iTerm, it returns a bit more sense making numbers




  • "supposed to be above" comes from estimated size in Time Machine preference pane
  • "actually 10 MB changed" comes from terminal tmutil compare result.


I think it's wrong it's backing up almost whole drive again. I know the backups consists of actual files and links to not changed files from previous backup. But the links should not consume same size as the linked file and according to free space after second backup the second backup is really consuming the space almost like first(full) backup (checked in disk utility)


I am using external USB drive


I tried:

  • reset Time Machine –
  • reformat the backup partition on external drive
  • check both Macintosh HD and backup partition in Disk utility while being in recovery mode
  • check if both Macintosh HD and backup partition are GPT and Mac OS X Extended (Journaled)


Question: How can i prevent Time Machine to make so big backups when actually 10 MB changed?

MacBook Pro, OS X Mountain Lion (10.8.2)
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