We remember when 80GB seemed like an unbelievably huge amount of storage for our Mac. But of course, 80GB now barely covers our collection of Simpsons episodes, not to mention all the other stuff we’ve got crammed in there. But your Mac can only hold so many hard drives. If you’re constantly pushing up against its limits or you want to add a heavy-duty backup, turn to an external RAID (redundant array of independent disks). These boxes let you expand storage with additional hard disks, even backing themselves up by writing the same data to multiple drives.