If anyone is planning to try this with the intent of getting storage performance, you should spend a bit more and get connectx-3 cards. Connectx-3 and newer support Network Direct which enables SMBDirect. You should come close to saturating the 40 gig link when using SMBDirect with lower cpu utilization than when using IPoIB.
Using connectx 2 as nothing more than an IPoIB adapter kind of defeats the purpose of using infiniband in the first place.