It is the hypervisor that shares the physical resources between the virtual servers; if the virtual servers are processing non-time-sensitive data, for example, serving a webpage or forwarding an email, a slight delay in processing might not matter. Lync Server deals with real-time audio and video, and the fact that it is real-time is key. Without consistent performance from the server, audio or video could glitch or freeze. Therefore, a virtual Lync 2013 server must perform consistently.
In Lync Server 2013 the load on the servers increases over Lync Server 2010:
• Gallery View now displays video of multiple conference participants simultaneously which impacts processing and network I/O.
• The presence database ...