I made a clone of my hard drive to an external drive and now I cannot boot to it.
What do I do?
You can only boot to an external hard drive that is connected via firewire to your Mac, to a Netboot volume, or a SATA drive connected via a PCI card. Only Intel-based Macs can boot to a USB drive. Note that a clone made from a Power PC Mac cannot be used as a boot volume on an Intel-based Mac and vice versa.
To boot to a firewire drive, go to System Preferences and choose "startup disk".
Then select the name of the drive you want to boot to. Click restart.
If you cannot boot to your internal drive and need a way to boot immediately to your clone, connect the clone to the computer via firewire, restart the machine and hold the option key. This will boot into the Mac's startup manager.
After a few moments, you should see icons of all bootable volumes your computer recognizes. Select the volume you want to boot to and click on the right arrow button.
It's always a good idea to test the clone right after you make it to make sure you can boot to it before you erase your internal drive.
Sometimes you cannot boot to your clone because you do not have the correct file permissions on the clone. To repair file permissions, open Applications > Utilities > Disk Utility and select the volume in the upper left part of the screen. Click Repair Disk Permissions. If you still cannot boot to your clone, you should reformat your external drive using Mac OS Extended (Journaled) format then create a new clone.