We've been using TokuMX for a while and I highly recommend others take a serious look there. It already contains the benefits cited for MongoDB 3 and more. Toku also has a release candidate for the new Mongo storage engine API named TokuMXse, though it's interesting to see that TokuMX proper still outperforms it: http://www.tokutek.com/2015/01/first-tokumxse-performance-nu...