My Book 4TB Won't Unmount on my Mac

Tried through Disk Utility but failed. Tired through Terminal to force it to unmount (diskutil unmountDisk force /Volumes/My Book) but failed. Help

  1. Restart your Mac with the WD connected

  2. Before Apple logo appears, press-hold Command + R to boot into Mac OS X Utilities

  3. In Utilities, go to Disk Utility and try to unmount the hard drive from there.