Hyper-V Replica and Riverbed document

This document captures the results from the bandwidth optimization experiments conducted in the Microsoft® Engineering Excellence Center (EEC) lab by using the Riverbed Steelhead appliance WAN optimization devices with Windows Server 2012 Hyper-V Replica.

So basically if you use Hyper-V replica across WAN you should use WAN optimizers in order to reduce traffic and bandwidth. You can see the results from the document here.