I had written an article previously explaining the HP & Dell sizing tools for Exchange 2007. HP has released a similar tool for Exchange 2010, more info here. Dell has followed the path and has released a sizing advisor tool for Exchange 2010. Unlike other sizing tools, Dell Advisor is an online one and hence solutions cannot be reused. The tool supports DAG and DAS/SAN based storage.
Access the Exchange 2010 Advisor here
