Time Machine - Frequently Asked Questions

9. Why are my backups so large?

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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 question #10.

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

A number of things can cause extra-large backups:


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

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

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

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

  5. 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 1 home folder). 

  6. 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 Troubleshooting item #A4.

  7. 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.

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