MS is very confusing on how they do clustering. They only can do "active/passive" clustering. Using MSSQL you can only have one active node for a given database. What that means is only one box can process database transactions at a time. What Active/Passive is means that you have one box or node processing requests while the other box "passive" waits in the shadows if the primary box fails. It has an "are-you-alive" connection to the primary server. If the primary server fails to respond that it is alive. The passive server takes over shutting down the primary server. What MS calls "Active-Active" is really two active passive setups. Each node(server) is primary on one database but a different database. Then if either database server fails the other server takes over processing for both databases. It is NOT parallel processing or most peoples interpretation of "active-active" MS re-defined active-active around their architecture. If you want active active parallel processing on the same database you have to go with Oracle which allows up to 4 servers to process transactions for a single database but this is really big bucks. Postgresql also allows similar active passive functionality with Sloany and it's a free database server. MS last I checked wants 100K for thier solution.
Find the MS white papers on this subject if you want to find out what it really does. They were writen by engineers not over hyped marketing folks. If you find the white papers please post them here in this forum.