Here's the summary of the issue and what Seagate is "admitted" of the problem: http://techreport.com/discussions.x/15863
Here's another:
http://www.tomshardware.com/news/seagate-barracuda-1-5TB-freezing,6558.html
But in my search of hard drives recently, I've run into many reports of having reliability issues even on the 1TB by Seagate, WDC, and Hitachi. The worst that I've seen reported was on on the Seagate 1.5T, which I've crossed off my list immediately. I guessed I will settle on the Samsung 1TB since it had the most favorable review - reliabilities and performance-wise. The Samsung isn't listed as a compatible drive for the DNS-323, but I'll try it out anyway.