Interesting - one drive is SD17, but the OTHER drive is CC1H.
I'll call Seagate later today. Will this wipe that SD17 drive of data? If so, would I just put in the DNS-321 as if it were a new drive and let it rebuild the raid array?
-- update -- I waited for a while to get through to seagate, and lo and behold, they do have the link posted in their knowledgebase. Updated the firmware and reinstalled it in the 321 and all data seems intact.
Now I'll give it some tests - hopefully this solves it!