I have read here on the forum that external drives need to be partitioned using the GUID scheme in order for them to be bootable.

I have two 1TB LaCie Big Disk Extreme+ drives. One is used exclusively for Time Machine, the other is partitioned using Apple Partition Map into three drives: one for data, the other two are for use by SuperDuper! for alternating nightly scheduled backups.

I was concerned after reading about the necessity of partitioning using GUID, so I booted my Macbook Pro while holding down the option key. I was able to select one of the two drives with SuperDuper! backups and booted up with no problem at all.

My questions:

• Am I missing something here?
  
• Should I repartition my Lacie using GUID?
  
• What is the advantage of GUID over Apple Partition Map?

BTW, I'm running OS X 10.5.5.

Thanks...

Lew