Spotlight stores its indexing data on the volume that is indexed in an invisible folder named .Spotlight-V100, so it isn't using any of the space on your startup drive. Put the volumes you don't want indexed into the Privacy pane of the Spotlight panel in System Preferences.
BTW, if your backups are on the same drive as your startup volume, that is, you have simply partitioned a single drive to have everything, just in different volumes on that drive, your backups won't do you any good if the drive fails. And they do fail sooner or later.
Francine
Francine
Schwieder