Advanced Virtualization Features

As these enterprise-class virtualization products have grown, more features have been added, enabling them to cluster physical host machines, move virtual machines seamlessly between hosts while still online, and manage virtual machines from a single console. Most of these features are similar between VMware and Hyper-V products, but have different names. This section covers those naming differences and describes the different features because they are referenced later and have a direct effect on support in Lync Server 2013.

• Failover Clustering/High-Availability—This refers to the capability to join multiple physical hosts into a cluster where shared storage from a storage area network (SAN) is provisioned. When running on a clustered set of physical hosts, a virtual machine can be made highly available. If a physical host fails or restarts at some point, the highly available virtual machines running on that host can be automatically restarted on a different host. The virtual machine is also restarted during this process, similar to the power being turned off and then back on.

• Live Migration/vMotion—This provides the capability to move virtual machines between different hosts in a cluster without any disruption of service or perceived downtime. For example, a virtual machine that is online and running can be migrated to another host while users remain connected to the virtual machine. This is accomplished by the host machines transferring the memory state of the guest over the network and then simultaneously bringing the machine online on the new host while the previous host removes its copy. Both host machines must remain online during this process, and the virtual machine remains available to users during the process.

• SR-IOV (Single-Root Input/Output Virtualization)—With SR-IOV, the control and management of a physical network adapter can be assigned directly to a virtual machine. This reduces I/O (input/output) overhead and increases performance. SR-IOV is supported in Windows Server 2012 Hyper-V.

• Dynamic Memory/Memory Overcommit—This involves the capability to dynamically change the level of physical and virtual memory allocated to a virtual machine. This enables the hypervisor to dynamically allocate resources to best meet the guest virtual machines’ requirements.

• Quality of Service (QoS)—QoS at the hypervisor level enables the provisioned virtual network to have an attached Service Level Agreement (SLA), enabling the physical network connection often shared between virtual machines to be configured to ensure that each virtual machine gets appropriate bandwidth.

• System Center Virtual Machine Manager/VMware vCenter—These two products are Microsoft and VMware’s respective centralized management suites. When a single hypervisor is used, management of the host and guest virtual machines can be done individually, but as more hosts and guests are added to an environment, managing each host separately can become tedious. These management products offer a centralized view and configuration store of all the hosts and guests within the virtualization environment.