Since Western Digital reported full compatibility, I ordered and
finally received 2 Western Digital REDs - WD20EFRX - 2TB drives.
Since I knew the drives were coming, my data was already backed up, so I formatted the old 500 GB Seagate drives, and moved them to my older DNS-321 and set them up in Standard mode.
Then I installed the 2 - WD20EFRX - 2TB drives in the DNS-325 and set them up running RAID 1.
I spent most of Sunday transferring my media back to the DNS-325.
I am happy to report all is working fine, and the DNS-325 has never been quieter.