Are USB Hard Drives bootable?

[macmanmk]

Originally Posted by dnanian

Not a problem, as long as the USB drive is properly partitioned (using the "GUID" partition scheme -- see the "Options" Button in the Partition tab of Disk Utility).

Well, there could be problems. I recently set up one of the new MacBooks and cloned it to three different GUID formatted hard drives...a Western Digital MyBook, a G-Technology G-Drive and an OtherWorld Computing Mercury Elite AL Pro drive. After cloning, the MacBook would absolutely not boot up from the Western Digital or G-Tech drives. It would boot up from the Other World drive. I saw the exact same behavior with a MacBook Air. Nobody has ever been able to explain why clones performed on three separate GUID formatted disks were not bootable on two of those three disks. I just think people should know that being able to boot from any old USB drive partitioned as a GUID disk is not a certainty.