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Original post by: mayer ,


You have a couple of problems here. While Macs are fine booting externally from a disk with any format, internally they MUST be formatted as GUID Mac OS X extended.  Your external is probably formatted MS DOS or FAT.

Second, when replacing the internal drives, the heat sensors on the Apple priority drives prevent just dropping in any off-the -shelf drive.  You will need to get an OWC 2011 thermal sensor to prevent run away fan issues.  Here's what you need: