As we noted in our introduction to this guide on virtualizing mission-critical applications, IT shops have begun to see the virtues of virtualizing resource-intensive applications. So can you virtualize your Microsoft Exchange servers? Should you? These are major questions in the worlds of virtualization and email administrators today. No matter which virtualization hypervisor you use, does Exchange make a good candidate for virtualization?
Your immediate answer to this question should be, "If virtulization makes sense in terms of performance." Above all else, if you can eke an acceptable amount of performance from a virtualized Exchange infrastructure, the intrinsic benefits of virtualizing (backups, disaster recovery and so on.) greatly outweigh the costs and added complexity.
With that statement in mind, however, consider the following five tips as important if you consider going down the road of virtualized Exchange:
Tip No. 1: Ensure supportability
Microsoft's support of Exchange in a virtualized environment holds true only when fairly specific criteria are met. Before considering any new virtual Exchange servers, ensure that you meet the following minimums:
- The hardware virtualization software used is Windows Server 2008 Hyper-V, Microsoft Hyper-V Server, or any third-party hypervisor that has been validated under the Windows Server Validation Program.
- The Exchange Server virtual machine runs Exchange Server 2007 SP1 or later, is deployed on Windows Server 2008, does not have the Unified Messaging server role installed, and meets the minimum hardware requirements for Exchange.
- The Exchange Server virtual machine uses fixed-size storage, SCSI pass-through storage or iSCSI storage. Microsoft does not support dynamically expanding and differencing disks for Exchange use.
Tip No. 2: Consider server consolidation ratios of 1:1
For many environments, the primary goal of virtualization is to consolidate as many virtual machines onto as many virtual hosts as possible. Squeezing 20 virtual machines onto a host (as opposed to 10) uses fewer physical servers to power your infrastructure, but it also means that more virtual machines vie for resource attention. That resource contention isn't a good thing for Exchange.
One of the benefits of Microsoft's Hyper-V solution is that it costs you nothing over and above the OS license you already have. This means that virtualizing an Exchange server can be done with your existing licenses. With that in mind, consider 1:1 as a consolidation ratio for your Exchange servers, where you have one virtual machine per physical host. By consolidating in this manner, you eliminate the possibility of resource contention while retaining the benefits of virtualization for your Exchange Servers.
Tip No. 3: Select a failover mechanism, but only one
Microsoft supports the use of Exchange Cluster Continuous Replication (CCR) as well as Single Copy Clusters (SCC), Local Continuous Replication (LCR), and Standby Continuous Replication (SCR) in virtualized Exchange environments. It also supports the use of hypervisor-based failover solutions such as Microsoft Live Migration or VMware VMotion. But it does not support using both of these technologies simultaneously. If you elect to virtualize your Exchange environment, choose one of these options for failover, but only one. Tip No. 4: Never snapshot Exchange
Snapshots are a great technology for creating an instant backup of an Exchange server; but these snapshots are not application-aware. While taking a snapshot and immediately reverting to that snapshot might appear to work flawlessly, there can be unintended consequences and potential data loss when snapshots are allowed to remain over a period of time. This is because of the state-based nature of Exchange data. As a result, Microsoft does not support the use of snapshots for Exchange servers. Tip No. 5: Be conscious of storage space
Remember that Hyper-V Virtual Hard Disk files cannot exceed 2,040 GB, which amounts to a size just short of 2 TB. While this might seem like a large amount of space, Exchange data stores can grow exceptionally large when unmonitored. Environments can circumvent this limitation by using iSCSI within a virtual machine to connect to data stores or by exploiting pass-through disks. These alternate approaches do not have the same limitations on disk space. About the author: Greg Shields is an independent author, instructor, Microsoft MVP and IT consultant based in Denver. He is a co-founder of Concentrated Technology LLC and has nearly 15 years of experience in IT architecture and enterprise administration. Shields specializes in Microsoft administration, systems management and monitoring, and virtualization. He is the author of several books, including Windows Server 2008: What's New/What's Changed, available from Sapien Press.