Customers have attempted to virtualize Microsoft Exchange Server since the earliest hypervisors appeared. At first, Microsoft resisted these attempts and would not provide support if problems appeared. The attitude was that any problem must be replicated on a “real” server before support was possible.
The situation changed with Exchange 2007. Customer demand, the growing maturity of virtualization technology and the appearance of Microsoft’s own hypervisor (Hyper-V) created a new imperative for Exchange to support virtualization. Since then, Microsoft has steadily improved the ability of Exchange to use different virtualization technologies and Exchange has become an application that is commonly run on Microsoft Hyper-V, VMware vSphere and the other hypervisors approved by Microsoft.
Virtualization creates its own particular technical demands that system administrators have to take into account as they plan its use with applications. Some applications, like Exchange, have relatively strict guidelines about the virtualization technologies that can be used and those that cannot. Sometimes this is because a technology is unproven with Exchange; sometimes it is because the way that the technology operates conflicts with the way that Exchange behaves. This document lays out the most important issues that system administrators should know about as they approach the deployment of Exchange 2013 on a virtualized platform.
Given the rapid cadence of updates with Microsoft’s release for Exchange 2013, the ongoing development of hypervisors, new capabilities in Windows and other improvements in hardware and software, the advice outlined here is prone to revision over time. It is correct as of April 2014 and covers Exchange 2013 SP1, Windows 2012 and Windows 2012 R2, and the virtualization technology available at this time.
Advocates of virtualization usually advance their case on the basis that virtualization allows greater utilization of available hardware. The idea is that one or more large virtual hosts are capable of providing the necessary resources to support the required number of Exchange servers. Tuning the virtual host allows precisely the right level of resources to be dedicated to each Exchange server, whether it is a dedicated mailbox server, a multi-role server, or a CAS or transport server. The advantages claimed include:
None of these advantages can be gained without careful planning and preparation of the virtual environment that will support Exchange. A badly configured and managed virtual environment will be even more fraught with problems than its physical counterpart. It is therefore critical to emphasize that it requires substantial effort to support virtualized Exchange. In the IT world, nothing good comes free of charge.