If you're using OS X El Capitan or later you may notice that Disk Utility looks and operates a bit different.
Ọ bụrụ na ị na-eji os X El Capitan ma ọ bụ mgbe e mesịrị, ị nwere ike ịchọpụta na Disk Utility na-ele anya ma na-arụ ọrụ dịtụ iche.