OS X Mountain Lion: Erase a disk
This article has been archived and is no longer updated by Apple.
You can erase a disk to use it again with Disk Utility. For more information, see this topic in Disk Utility Help:
Erase a disk, CD, or DVD
Warning: Erasing a disk permanently deletes all files on the disk. Before you erase a disk, copy any files that you want to keep to another disk or to removable media.
Last Modified: Sep 4, 2015