Server virtualization brings numerous benefits, including hardware consolidation and flexibility, and can lower both capital expenditures and operational costs. Exchange Server can be deployed as one or more virtual machines (VMs) mounted on physical host servers, but Exchange Server is a complex and demanding application. Virtualized Exchange success requires careful planning as well as a keen awareness of potential pitfalls.
Consider the principal advantages of server virtualization: It improves server hardware use and allows more workloads to run on the same physical box. Instead of following the traditional "one app, one server" paradigm, a physical server can host numerous VMs.
Virtual workloads are also more flexible and can be moved easily from one physical server to another without reinstalling or reconfiguring the application. This capability greatly eases troublesome issues like server maintenance, high availability and disaster recovery. Additionally, an Exchange administrator can adjust the amount of computing resources allocated to each VM in order to ensure stability and optimize performance.
The mailbox role is very I/O intensive for Exchange, and I/O operations are one of the most problematic types of activities in a virtualization environment.
Enterprise infrastructure architect Planet Technologies, Inc.
Exchange Server leverages all of these capabilities when virtualized. The multiple-role architecture of Exchange Server 2007 and Exchange Server 2010 give administrators a good deal of control over how individual server roles are virtualized and distributed onto physical servers. "In smaller environments, you can have all of these services [server roles] on one box," said Mike Crowley, enterprise infrastructure architect for Planet Technologies, Inc., a Germantown, Md.-based IT consulting and services company.
Virtualizing Exchange Server is not an all-or-nothing proposition. In some circumstances, you can elect to leave the most critical server roles such as the mailbox server and unified messaging role nonvirtualized on traditional servers. You may, however, choose to virtualize other roles -- client access server, hub transport server and edge transport server -- and deploy them onto one or more additional servers. For example, rather than deploying five traditional servers, each with a single Exchange Server role, you may only need two or three suitable servers.
Virtualization supports a redundant iteration of a VM on two or more different physical servers, improving high availability. If one server fails, the redundant VM steps in and takes over without hesitation. This is a bit different than traditional server clustering, and is an accepted practice in virtual Exchange environments.
Similarly, a VM on one failed server can be moved to or restarted on another suitable server in just a few minutes. The availability isn't quite as good when migrating or restoring VMs, but it's another useful tool that Exchange administrators can rely on to keep an environment running.
Installing Exchange Server in a virtual environment
The requirements and approach to Exchange Server deployment in a virtual environment are fundamentally identical to those used in traditional nonvirtualized systems. The biggest issue in Exchange virtualization, however, is that you must meet or exceed the hardware requirements of the components being deployed. This isn't an issue for traditional servers because today's server hardware will easily provide enough computing resources to accommodate the role that's installed.
As more virtual servers are deployed to the same box, the demands on CPU, memory and I/O resources are cumulative. Because of this, it's much easier for the computing demands of the VMs to overwhelm the associated physical server. This inevitably leads to poor performance of the Exchange Server roles or even a VM crash.
An Exchange administrator has some latitude when allocating unused computing resources, but that won't fix a resource shortage on the box. For example, you'll run into trouble if you need 10 CPU cores to run Exchange Server roles, but the box only has eight cores.
"The mailbox role is very I/O intensive for Exchange, and I/O operations are one of the most problematic types of activities in a virtualization environment," Crowley said. "So that is often a role that ends up being on a physical box."
Andy Grogan, Exchange Server MVP, said there are a few more limitations to consider. Grogan advises admins avoid combining mailbox, hub transport and client access server roles on the same guest because this configuration exceeds the number of virtual processors that can be allocated. Additionally, it's not always possible to recover Exchange correctly from a snapshot, so you should implement other data protection schemes.
Exchange Server 2010 database availability groups (DAGs) are not supported natively with VMware Inc. vMotion, Microsoft Hyper-V Live Migration or Citrix XenMotion, which makes VM migration problematic for DAGs. These are just a few of the potential pitfalls that can snarl a move to virtualization for Exchange. Microsoft offers comprehensive documentation on the various scenarios for virtualizing Exchange Server.
Protecting and managing virtualized Exchange Server
Virtualization itself does not change your current Exchange Server backup scheme; you can usually continue to protect Exchange VMs using the same methods you used for nonvirtualized servers. You can also use tools like as Microsoft's System Center Data Protection Manager or Exchange Server 2007's standby continuous replication (SCR).
However, virtualization can provide additional ways to protect Exchange Server and ensure continued high availability. VMware environments, for example, can use VMware Consolidated Backup (VCB) to protect virtual machines.
Snapshots of Exchange VMs are potential options, but restoring Exchange Server snapshots can be problematic. "It doesn't always work; it's really finicky based on time stamps," said J. Peter Bruzzese, Exchange Instructor for Train Signal. "Trying to fit a server back into an environment that isn't up to date with everything else that's been happening can be tricky."
Virtualization also does not necessarily change Exchange Server management. Administrators can continue to use Exchange Management Console (EMC) or Exchange Management Shell (EMS). "From my perspective, those tools [EMC and EMS] can be installed on a Windows 7 client, and I can manage my Exchange environment from anywhere," Bruzzese said. "So, management of Exchange hasn't changed even though it's all virtual."
However, virtualization does add another layer of management in that administrators may want to turn to platforms like System Center Virtual Machine Manager (SCVMM) to maintain control of all VMs and computing resources in their environments. For example, an administrator may use SCVMM to adjust computing resources allocated to an Exchange Server VM. But that method isn't really managing Exchange; that's managing virtualization.