I’m running a pair of 500GB LaCie drives in RAID 1 set that got out of sync recently during a hardware failure that resulted in Apple replacing my logic board. I first noticed this because Disk Utility listed my RAID set as ‘degraded’. Simple enough to fix, I thought, and clicked the Rebuild button. Wrong.

Turns out there is a bug in Leopard’s Disk Utility whereby you must use the command line to rebuild degraded RAID sets. If you are getting the infamous ‘Unrecognized Filesystem’ error when you try to rebuild your RAID set follow the instructions below.

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