Specifications

Best Practices for Virtualizing and Managing Exchange 2013

Figure 32 shows how SR-IOV attaches a physical NIC to an Exchange 2013 virtual machine. This provides

the Exchange 2013 virtual machine with a more direct path to the underlying physical network adapter,

increasing performance and reducing latency—both of which are important considerations for the

Exchange 2013 workload.

Figure 32: SR-IOV support in Hyper-V

With the virtual machine now attached to the physical NIC through the VF, does this mean that this

particular virtual machine cannot be live migrated to another physical host? The answer is no—the virtual

machine is still free to be live migrated, with no downtime, to another available node in the cluster. This

helps to ensure that Hyper-V in Windows Server 2012 not only provides high levels of performance, but

also does so without sacrificing agility.

SR-IOV automatically fails over the network traffic from the VF to the synthetic data path of the Hyper-V

virtual machine. The transition between the VF and synthetic data paths occurs with minimum loss of

packets and prevents the loss of TCP connections. Whenever there is a state transition that requires the

hardware state to be saved, the VF is removed from the virtual machine beforehand, falling back to the

synthetic path. Once the VF is removed, any operation necessary can be performed on the virtual machine

because it is a complete software-based container at that point.

The Hyper-V child partition is being live migrated to a different host at this stage. Once the operation has

been completed, assuming hardware resources are available and other dependencies are met, the VF is

returned back to the virtual machine. This solves the problem of saving the hardware state of the virtual

machine and helps to ensure that workloads receive the highest levels of performance. The high-level

process is outlined below.

Note that throughout this process, the Exchange virtual machine always

has connectivity.

 SR-IOV is enabled for the Exchange virtual machine, and its VF is assigned. Traffic flows down the

VF path, not the software stack.

 When live migration starts, connectivity is failed over to the synthetic path, and the VF is removed.

 At this point, live migration of the virtual machine takes place from source to destination. (Traffic

is now travelling via the synthetic software stack.)

 Upon arrival, the VF is reassigned and traffic now passes via the VF. Alternatively, if the virtual

machine has been migrated to a new host that does not have SR-IOV-capable hardware, the

network traffic continues to operate along the synthetic software stack.