Well, I'm learning more and more about this product, things that Tech nonSupport doesn't know, or doesn't want to reveal. Their answer to everything is clear out the cache and reformat.
I took two 750 Gig HDs on their approved list (see my initial post for the model numbers) and low-level formatted them (12-14 hours each). Stuck them into to the DNS-321, turned off my pop-up blocker (as suggested in another thread), cleared my cache and attempted another standard format, and it hung at 94% again. What a surprise.
I then attempted the same format from a Linux box running Red Hat (version 4.0, if I remember correctly). I was stunned to see it actually complete something. (In my best Church Lady voice)... So, who can we blame? Who on earth, in heaven, or in Hades can we blame? Could it be.... SATAN?
Okay, some of the other posts that I've read on this and similar D-Link devices indicates that IE 7 might be the problem. Rather than me spending a lot of time trying to do the jobs of the Tech nonSupport people and solve the problem globally, I thought I'd move on. I attempted another format, one with a 100 Gig RAID 1 setup, with the rest of the space on the two hard drives set as standard volumes. It failed once under Linux (at 94%), so Satan isn't completely to blame, but it did pass the second time that I attempted.
After all that I've read on this and similar devices, I decided against running with a RAID 1 setup. I would rather do scheduled backups every day, so that if something is inadvertently deleted, it can be recovered if it is caught before the next scheduled backup. There were just too many people complaining that a RAID disk when down and they lost ALL of their data on both disks, or similar problem.
I still can't recommend this device to anyone, but if you already have one, or HAVE to have one, this information might help you get it working.
Good luck. You are going to need it.