You can mix physical and virtual servers in your deployment, with only the following restrictions:

• You cannot mix different types of servers within the same pool. All servers within the same pool must either be physical or virtual. For these purposes, Front End Servers and SQL Servers running the back-end database are considered to be separate, meaning that you can have virtual Front End Servers using a physical back-end database.
  
  This is the only limitation to mixing physical and virtual servers. You could have one Front End pool of physical servers and another of virtual servers. And you can deploy different pools and servers as either physical or virtual in any combination.
  
  
• All servers within one pool should provide about the same performance. For example, if you have virtual Front End Servers in one pool being hosted on different host servers, you should make sure each virtual Front End Server is capable of a similar level of performance.
  
  

If you are deploying a large amount of virtualized servers across different host servers, you should consider spreading out the members of one pool across different host servers. For example, in a pool of eight virtual Front End Servers, deploy four on one physical host and four on another. While this is not a true high-availability solution, it does provide some protection if a single host server fails.

The following table shows the recommended base hardware for a host server.

Both the physical host servers and all virtual servers must run Windows Server 2008 R2 with the software update described in Microsoft Knowledge Base article 981836, "Network connectivity for a Windows Server 2003-based Hyper-V virtual machine is lost temporarily in Windows Server 2008 R2," at http://go.microsoft.com/fwlink/?LinkId=201212.

Note:
You must run this update on both the physical host server and all virtual machines, even though the Microsoft Knowledge Base article states otherwise.

Lync Server provides real-time communications, and depends on fast and efficient networking. If a packet is delayed by as little as a few milliseconds, users might detect an audio glitch, experience a delayed call, or frozen video. To improve the network performance of your virtualized topology, you should do the following:

• The host must have at least one network adapter dedicated to the virtual machines running Lync Server roles. Sharing a network adapter with the host or with a storage area network (SAN) is not recommended.
  
  
• Note that a Lync Server workload that includes media (Front End Servers and A/V Conferencing Servers) can reach a peak network utilization of more than 500 Mbps.
  
  
• If one host server is running multiple guest virtual servers that each run Lync Server media workloads, ensure that the host network adapter can handle the traffic. To prevent bottlenecks, consider a higher speed network adapter (such as 10 GbE) or multiple network adapters using link aggregation.
  
  
• Enable virtual LAN (VLAN) tagging on the network adapter, and implement multiple VLANs on the virtual servers to optimize network traffic.
  
  
• Implement multi-path I/O (MPIO) to your back-end database.
  
  
• Use network adapters enabled for Virtual Machine Queue (VMQ). VMQ is a virtualization technology for the efficient transfer of network traffic to a virtualized operating system. VMQ allows the VMs to filter the queue of packets within the network adapter, resulting in improved efficiency of network traffic. If you use these network adapters, you can enable VMQ for each virtual machine using the hypervisor’s management console.
  
  

To provision enough virtual servers for your needs, use the following table to compare recommended scalability of physical and virtual specifications for Lync Server 2010 roles.

We recommend you use Microsoft System Center Virtual Machine Manager (VMM) to manage your virtualized Lync Server topology.

By using VMM, you do not need to use Terminal Services or Remote Desktop Services for the virtual machine management. Additionally, by using VMM you can view and manage performance, and other components such as disk space. You can also save a virtual machine as a template for creating new instances.

VMM uses Windows PowerShell, so you can create VMM Windows PowerShell scripts that integrate with Lync Server Management Shell to manage Lync Server.

For details about VMM, see the System Center Virtual Machine Manager website at http://go.microsoft.com/fwlink/?LinkId=202887.

Getting Started Using VMM

You can use Microsoft System Center Operations Manager (formerly Microsoft Operations Manager) to monitor your virtualized topology, just as you can with a physical topology. If you do so, install System Center Operations Manager R2 first, add the Lync Server Operations Manager pack, and then integrate it with VMM.

For details about integrating System Center Operations Manager with VMM, see "How to Integrate Operations Manager with VMM 2008 R2" at http://go.microsoft.com/fwlink/?LinkId=201214.