But at the end of the day I, too, found Disk Utilities RAID functionality too problematic to use. This document will be updated as more information becomes available. MacBook Pro (not including MacBook Pro (Core 2 Duo) models).The following computers do not support booting from software RAID volumes: If you try to start these Intel-based Macs up from a software RAID volume, the computer may start up to a flashing question mark. Some Intel-based Macs do not support booting from software RAID volumes. Intel-based Macs: Flashing question mark when trying to boot from RAID volume RAID booting is supported on some Macs (your Mac), but not all Macs. Not quite as secure, but a lot less hassle! If you don't have an XServe and you really, really want a RAID, it appears that SoftRAID may be the best solution.
I gave up on the RAID idea and instead have scheduled SuperDuper! to periodically make a Smart Update image copy of my boot drive to the external drive. In fact, in Snow Leopard, they don't accurately reflect the operation of the program: I saw a Demote button on the RAID setup panel that wasn't even mentioned in Help, and some of the RAID procedures described in Help simply didn't work. None of Disk Utility's help files give you any warning about this. I successfully used a mirrored RAID on an older G4 Tiger system with two internal drives, but according to the folks at SoftRAID, Apple's software RAID is basically intended for XServes and isn't even tested on external drives.
I finally gave up as the external partition was getting constantly corrupted (and the advertised "automatic rebuilding" didn't work). I just wasted a couple of days trying to make Apple's Disk Utility RAID tool create a mirror of my Mac Mini's internal drive on an external FireWire drive.