Tip: Spotlight and backup disks

If you have a hard disk that you use for backing up, say with Carbon Copy Cloner or SuperDuper!, I suggest you add that volume to the Spotlight Privacy list, as not only will you duplicate your index size, but the system will try to index the volume as it’s being indexed by Spotlight.

This means that you won’t be able to search the volume, but should you need to, you can enable spotlight and let it index then.

Spotlight Privacy