If you've upgraded to El Capitan in OS X, apparently Disk Utility has been revised also and is not as robust as previous versions. If you feel the need to revert to the earlier version, here is an article describing how to do so. Be aware, this is not for the faint-hearted. Also, be sure to read all the comments at the end of the article because corrections and permutations of the original instructions follow from readers all around the globe.
Jim Hamm