Backup 3.0.x (#6): Explanation of incremental backup mechanism, tips

As we've covered in a number of previous reports, Backup 3.0.x is the first iteration of this Apple utility that sports the ability to perform incremental backups.

When you first use Backup 3.0.x to perform a data duplication, it performs a full backup, in which all files and folders are replicated. By default, during subsequent backup routines, incremental updates are performed. Each incremental update includes data reflecting the changes that have been made to files and folders since the prior incremental backup. However, each backup is not wholly inclusive. In other words, assume there are three backup files -- the initial full backup (A), and two incremental backups produced thereafter (B and C). Assuming backup C comes after backup B chronologically, backup C it will include only the file changes made between backups B and C -- not all of the changes made since the full backup. So, if you delete incremental backup B, you will be losing file changes and potentially new files created between the full backup (A) and backup B.

The problem many users are running into, as noted in a previous report, is that Backup 3.0.x provides no way to automatically delete old incremental backups. In past versions of Backup, the application would always perform a full backup, overwriting the files each night -- meaning your backup disk usage would only mimic the usage on your active disk. With incremental backups, however, users can find themselves running out of space quickly.

MacFixIt reader Joe writes:

"I may be doing something wrong, but Backup 3.0.x leaves hundreds of .IncrementalBack suffix'd files in my back up folder dating back several months. I run a set that includes my Eudora folder and personal settings daily. Backup leaves the past days files on my iDisk, which I guess is for rollback, but seems really wasteful when I see files going back to Sept. 25th and it is nearly Dec. 25th.

"The biggest downside is that I'm running out of space on a regular bases, backups fail and I wind up manually just deleting those files and manually running a full backup of each item to start over again."

The best method of dealing with these storage concerns -- though Apple should definitely consider adding an automatic "clean-up" routine to Backup -- is to simply use the "Remove iDisk Backups," menu option (or manually delete files from the backup target disk) on a periodic basis, then start over with a new full backup.

If you are making massive file modifications daily, or adding new files at a rapid pace, you may want to consider using only full backups. This way no space will be wasted with incremental files created during each backup, though the backup process will be much longer each time.

Feedback? Late-breakers@macfixit.com.

For more troubleshooting information, see our Backup product page.

Previous coverage:

• Backup 3.0 (#5): No way to automatically delete old incremental backups
• Backup 3.0 (#4): More on 'Backup archive in use' message -- workaround; Backups cannot be resumed
• Backup 3.0 (#3): Incomplete restores; Backup archive 'in use' message
• Backup 3.0: Review, troubleshooting issues

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