I have it formatted in Mac OS extended(journaled) and its partitioned as GUID. Even with that done I still can't boot up using it. It doesn't show when i start up holding down option key. So my question is can you a USB external drive to boot from?
I got it to work. I had to put the generic OS X on the external. I was trying to do something with the Air and trying to use its install disc but it doesn't have firewire and I couldn't get the disc to install on other Mac's.
To get the external HDD to boot it is necessary to format in Apple Partition Map. Connect the drive and when it appears on the desktop you will have to use Disk Utility to make it Apple Partition Map and not OS Extended.
After backing up your system using utility such as SuperDuper, it is the best, the disk should appear in Startup Disks in the System Preferences. You can then boot from USB2 Intel and Firewire PPC.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.