I've done some quick Googling but didn't find an answer. I've put an SSD in my Macbook, and at the same time moved the original hard drive to the optical drive bay. I'm running the OS and most of my daily apps off the SDD so the hard drive is really just for storing stuff I need now and then.

Now I'd like to disable (as in power off or "force sleep") the hard drive when I don't need it. Tried unmounting the disk using diskutil unmountDisk but it kept spinning for like 10 minutes. Maybe that's to be expected, but I'd imagined it would stop instantly on unmount. Also, it would be nice to have it disabled by default, and only mount it (= power on) when I need it.