Time Machine keeps doing full backups I keep seeing Time Machine doing a full backup of my ~80 GB hard disk. I see this a few times a week, when I first turn on my mac. During the day, I see Time Machine doing small incremental backups of ~100 MB, hourly.

Why does Time Machine does these big backups?

I also see the large backups in the logs here.

nanceki@Stephen-Nancekivells-iMac /v/log&gt; bzcat system.log.* | grep backupd | grep Copied | grep GB| sort | less

Jul 23 08:46:32 Stephen-Nancekivells-iMac com.apple.backupd[7569]: Copied 0 bytes of 78.3 GB, 0 of 23051 items
Jul 23 08:47:31 Stephen-Nancekivells-iMac com.apple.backupd[7569]: Copied 5324 files (1.1 GB) from volume Macintosh HD. 
Jul 24 08:55:37 Stephen-Nancekivells-iMac com.apple.backupd[20310]: Copied 0 bytes of 78.4 GB, 0 of 23013 items
Jul 24 09:52:18 Stephen-Nancekivells-iMac com.apple.backupd[20310]: Copied 24172 files (78.4 GB) from volume Macintosh HD. 
Jul 28 13:43:25 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 0 bytes of 76.5 GB, 0 of 4557 items
Jul 28 15:43:43 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 20.4 MB of 76.5 GB, 2477 of 4557 items
Jul 28 17:43:59 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 305.8 MB of 76.5 GB, 5797 of 5797 items
Jul 28 19:45:03 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 1015.8 MB of 76.5 GB, 5797 of 5797 items
Jul 28 21:44:58 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 1017.8 MB of 76.5 GB, 5797 of 5797 items
Jul 28 23:45:22 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 1.4 GB of 76.5 GB, 5797 of 5797 items
Jul 29 01:45:40 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 1.8 GB of 76.5 GB, 5797 of 5797 items
Jul 29 03:46:08 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 2.4 GB of 76.5 GB, 5797 of 5797 items
Jul 29 05:46:26 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 2.8 GB of 76.5 GB, 5797 of 5797 items
Jul 29 07:46:47 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 3.4 GB of 76.5 GB, 5797 of 5797 items
Jul 30 03:50:41 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 4.1 GB of 76.5 GB, 5800 of 5800 items
Jul 30 05:51:07 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 4.4 GB of 76.5 GB, 5800 of 5800 items
Jul 30 07:51:20 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 4.8 GB of 76.5 GB, 5800 of 5800 items
Jul 30 09:02:00 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 5.4 GB of 76.5 GB, 5800 of 5800 items
Jul 30 09:55:30 Stephen-Nancekivells-iMac com.apple.backupd[98930]: Copied 6598 files (76.5 GB) from volume Macintosh HD. 
Jul 31 09:09:22 Stephen-Nancekivells-iMac com.apple.backupd[4793]: Copied 0 bytes of 76.5 GB, 0 of 4510 items
Jul 31 10:03:35 Stephen-Nancekivells-iMac com.apple.backupd[4793]: Copied 5615 files (76.5 GB) from volume Macintosh HD.
Time Machine doesn't normally do that. Open Console (under Applications/Utilities), select All Messages in the log list, and type "backupd" into the filter bar. If you scroll back up to the time of one of these full backups, there may be a log message explaining why it backed up so much.