Q: Is it true I can't use Receive Side Scaling when Hyper-V is enabled on Windows Server 2012?
A. Receive Side Scaling (RSS) is a great technology that is necessary when you move from 1Gb links to 10Gb links, as typically a network connection is processed only by a single processor core. For 1Gb, a single processor core can handle the network load; however for 10Gb, a single core would become a bottleneck. RSS allows the network load to be scaled across multiple processor cores on the system, enabling full utilization of the available bandwidth.
After the Hyper-V role is enabled, RSS is disabled as Hyper-V and RSS are mutually exclusive. Still, there is a silver lining. Hyper-V has support for Virtual Machine Queues (VMQ), which is a feature most server network adapters support.
VMQ allows each virtual machine (VM) (up to the number of VMQs supported on the adapter) to have its own transmit/receive queue on the network adapter, which allows the traffic for VM1 to be processed by one processor core, VM2 by another processor core and so on. It achieves a similar result to RSS but it is dependent on your network adapters supporting VMQ.
With Windows Server 2012 Hyper-V, the assignment of VMQs is performed automatically to VMs based on which ones will derive the most benefit from having a VMQ, dynamic VMQ. Note VMQ is ONLY used when Hyper-V is enabled.
This means VMQ and RSS are mutually exclusive but as long as you are using one of them your network load is balanced between processor cores.