NoSQL DB's like Cassandra are good at scaling out rather than up, more so than SQL Server. It allows a dept to move away from expensive big-iron SANs and just scatter your data across dozens of commodity servers. In theory, one could save significant money with the licensing costs (zero for Cassandra vs. ~25-30K per socket for SQL Ent.) and on hardware (no SANs, no wasted servers on MS clustering). But, Cassandra is not ACID compliant so data integrity is not implied nor guaranteed. It may also require more manpower to manage as with most open-source applications unless you employ only rock stars. As far as the volume it can handle, I don't have a clue.