I bought the 100GB Seagate drive for $40 (after rebate from Circut City) and I’m going to use that as my intermediate disk to replace the WD drive with the Hitatchi in my RAID array. I only have ~65GB to transfer, so the Seagate will work just fine.
Using a 4th drive for the transfer certainly simplifies the process a bit. Instead of the 9 step process I had planned, I only have to:
- Put new Seagate HD in external enclosure.
- Use Carbon Copy Cloner to copy my current RAID HD to the new external HD.
- Boot from external HD – make sure all looks right.
- Swap the WD HD and the new Hitatchi HD in the internal bay.
- Use Disk Utility to RAID the 2 internal Hitatchi drives.
- Use CCC to copy the external WD drive back to the new RAID set-up.
Much better. At some point I’ll get an enclosure for the SATA WD drive I guess… maybe I should just sell it since I don’t trust it.
Carbon Copy Cloner is doing its thing right now – I’m going to let it run overnight and hope all is well in the morning.
UPDATE: 2 hours late, looks like it’s about 60% done.
UPDATE #2: CCC reported a successful clone this morning, and sure enough, I just booted up with it. Everything looks good. 
I’m going to see about setting up the new HD in my RAID array, then cloning everything back.
UPDATE #3: I swapped the WD and Hitatchi drives and created my “all Hitatchi” RAID 0 array. Booting up from the Seagate worked just fine again. I’m now CCC’ing the Seagate to the RAID array.
UPDATE #4: The clone process I’m guessing took 4-5 hours to go from the internal RAID to the external drive took a mere 45 minutes going back from the external drive to the internal RAID array. Everything booted up and looks right!