[NSUserDefaults]

In that case you are supposed to use your /other/ backup. Which you have.

[DaSHacka]

Defeating the point of deduplication...

[homebrewer]

You don't have backups if you only have one "backup". Look up sysadmin's 3-2-1.

[NSUserDefaults]

On a single drive, deduplicate all you want. But you need to have two drives, at least, anyway.