It can only be enabled on a single drive containing OS X and Recovery partitions. The disk will be encrypted once you enter your password of choice-be sure to use a secure one! FileVault 2 cannot be used with every Mac and all drive configurations. Ctrl+click or right-click the drive in the Finder sidebar and select the Encrypt option. To encrypt a drive, simply open the Finder and connect the drive to your Mac.
In the resulting window, give the card a new name (or the same name it had), select Mac OS Extended from the Format drop-down, and select GUID.
