Time Machine - Troubleshooting

D4.  My backups seem too large

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A number of things can cause extra-large backups:

  1. By default, Time Machine will back up all internal disks/partitions that are formatted for a Mac (any variant of Mac OS Extended). If you have multiple internal HDs and/or partitions, and don't want them all backed-up, exclude those via Time Machine Preferences > Options.  See Time Machine FAQ #10 if you're not sure how to do that.

  2. By default, Time Machine will not back up external HDs, unless they've been removed from the exclusion list.  If you have any, check the exclusion list as above.

  3. Time Machine may be doing a full backup of your entire system. See item #D3.

  4. Erasing a disk/partition that's excluded in Time Machine Preferences > Options may remove it from the exclusions box, so Time Machine will try to back it up.

  5. Doing an OSX update can cause a large backup, as it may add or update many thousands of files.

  6. Removing exclusions, such as your top-level System and/or Library folders, can be sizable.

  7. Renaming or moving a file or folder causes the entire item moved or renamed to be backed-up, including all files and sub-folders (except in a File Vault home folder).

  8. Sometimes a corrupted preferences file can cause things to be backed-up that didn't actually change.  Try a "full reset" of Time Machine, per item #A4.

  9. If you use the ResetPassword facility to reset the permissions and ACLs on a user home folder, each item it actually changes will be backed-up on the next backup.

  10. There are some applications that can, in some circumstances, cause large backups.  See Troubleshooting item #D8 for details.

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There may be ways to minimize the size of such backups; search and/or post in the appropriate Apple forum for help:

OSX Mountain Lion 10.8

Mac OS X v 10.7 Lion

Mac OS X v.10.6 Snow Leopard

Mac OSX v.10.5 Leopard   

One solution is to simply exclude the item from Time Machine so it isn't backed-up regularly, then when you do want it backed-up, just copy it somewhere that's not excluded.  See Time Machine FAQ #10.

You can use the Time Tracker or BackupLoupe apps (see item #A2) to see exactly what was copied on any particular backup.