Disable Spotlight Indexing on a Volume in OS X Revision as of Monday, 21 December 2015 at 02:30 UTC

Like a Man

Let’s say our drive is called (and mounted as) Backup Drive. Open up a
terminal window:

 cd "/Volumes/Backup Drive"
 touch .metadata_never_index

Et voila!

Via System Preferences

1. Go to System Preferences > Spotlight > Privacy
2. Drag the volume into the list
3. Ta da!