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How do I use tmutil to figure out what is wrong with my Time Machine as it keeps backing up huge amounts of data each time it back-ups although nothing has changed since the last back up? I'm backing-up to a Drobo FS

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Have you checked it is backing up to the same location, with in the drive, or is it making a new back-up? – Graeme Hutchison Nov 16 '11 at 13:23
How do I check that? – Camilla Nov 16 '11 at 13:30
look in the destination folder and see if there are duplicate files. Have you done a full system backup overnight before? – Graeme Hutchison Nov 16 '11 at 13:47
up vote 2 down vote accepted


tmutil listbackups

to get a list of existing (completed) backups.

Then run one or both of

tmutil compare # to compare current drive to latest backup
tmutil compare /one/path/from/list /other/path/from/list # compare two backups
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You can use timedog to see what's being backed up each time.


  • Open Terminal (in /Applications/Utilities)

  • cd /Volumes/Time\ Machine/Backups.backupdb/[Computer Name] Note Time Machine may be different on your system. Replace [Computer Name] with the name of your computer (see System Preferences => Sharing).

  • /path/to/timedog -d 5 -l For instance, if you unzipped timedog to your Desktop, the path would be ~/Desktop/timedog

And then look at the output

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