Some people may experience issues with Time Machine reporting that the backup they intend to make is too big for the designated backup volume. Time Machine analyzes the data that is about to be backed up and compares it with the space left on the backup drive. Occasionally, this calculation seems to produce errors, despite the backup volume having plenty of space remaining.
MacFixIt forum user 1Seymour writes:
"I am running a Macbook Pro, Mac os 10.5.6. The error I get is backup is too large for my backup volume. Time machine says it wants to backup 408.2 GB from my half full 200 Gb drive? What can I do to reset Time machine?"Resetting Time Machine
1. In the Time Machine System Preferences, turn off Time Machine.Be sure to check your anti-virus software. MacFixIt "MacWizard" jchuzi relays:
2. Access your backup volume and delete the current backup file. Note: you will be without a backup of your data until Time Machine recreates your current drive's backup. Your new "latest backup" will be for the initial backup you are about to complete.
3. Access: Macintosh HD > Library > Preferences > com.apple.TimeMachine.plist and delete it.
4. In the Time Machine System Preferences, click "Change Disk..." and choose your backup volume.
5. Turn Time Machine on and let it complete its initial backup.
"I had had a problem with Intego Virus Barrier interfering with TM (not the same issue as yours, however). If you have any AV software running, disable it when TM makes its initial backup. I only had an issue with the initial backup, not subsequent ones."Resources
Read this MacFixIt forum thread on resetting Time Machine.
Read this Apple KB Article regarding Time Machine no longer backing up.
Experiencing problems? Have feedback? Let us know!Resources