Not sure if anyone has read this article that Apple posted in September, but it is an easy read and has some good information on ways to get around the 2 TB limit for LUNs. It adds a layer of complexity to structuring your storage pools but can keep you from loosing up to 3 TB per XRAID. So if you are still running Storage Pools with Affinities mapped for swap/render data rather than taking use of your whole XRAID, check it out.
http://docs.info.apple.com/article.html?artnum=302383