The question on many people’s minds has been answered. Yes, you can virtualize Exchange Server 2007 on XenServer. To go one step further, the results of our recent performance and scalability tests for Exchange Server 2007 with Citrix XenServer demonstrate that not only can you do it, but there are some very compelling reasons why you probably should. Here’s why…

Exchange adminstrators have always had to work within a fairly narrow range of limitations from Microsoft when it comes to sizing single or multi-role Exchange servers. While Microsoft’s intentions for these sizing limits is likely to obtain maximize performance while minimizing the points of failure that might affect users, the practical reality of those sizing guidelines is a limited ability to take advantage of the ever-increasing capacity and power of today’s server hardware. That means that when the enterprise needs to add users, it usually means adding more servers; and we all know how challenging that can be these days. By virtualizing Exchange Server 2007 with Citrix XenServer, administrators now have the ability to operate their Exchange Server farm within Microsoft’s sizing guidelines while using XenServer VMs as building blocks to achieve the scalability that isn’t possible in a physical Exchange Server environment. 

In our technical whitepaper entitiled “Virtualizating Microsoft Exchange Server 2007 with Citrix XenServer“, we demonstrated that Exchange Server virtualizes very well on XenServer. Not only did virtual Exchange Servers running on XenServer exceed Microsoft performance recommendations in every performance category, but in many cases virtual Exchange servers exceeded the perfomance of their native server counterparts! Here’s an example of what I mean. This was taken from the latest tests we just completed using Exchange Server 2007 VMs with Windows Server 2008 on XenServer 5.0:

Click on the above image to see the full size chart
In terms of SendMail latency, Microsoft’s recommendations are for less than 500Ms average latency and less than 1,000Ms in the 95th percentile. In the above results chart, we see that the SendMail latency performance measurements of the four virtual Exchange servers we tested was less than that of the native Exchange servers they were compared to. Results were consistent for both the 2,000 and 4,000 heavy user mailbox tests. Scalability tests measuring SendMail latency for up to 8,000 heavy user mailboxes was just as impressive, especially considering the 8,000 heavy user mailbox workload on a single XenServer host.

Click on the above image to see the full size chart

Results were equally as impressive in each of the other performance measurements categories we tested for, including Disk IOPS latency, CPU utilization and RPC latency.

So, now we know that the overhead for virtualizing Exchange Server 2007 on XenServer is very low and that when doing so Exchange Server 2007 performance is remarkably solid. One challenge solved. But what about reliability and availability? After all, Microsoft Exchange Server is nearly always viewed as one of the more mission-critical applications in the data center. XenServer addresses availability and reliability using our live VM migration feature, XenMotion (free with XenServer Enterprise Edition), together with the High Availability features that come with Citrix Essentials for XenServer. Our tests showed that active Exchange Server VMs were easily migrated between XenServer hosts with no loss in performance whatsoever. Tests also showed that after “protecting” VMs using XenServer’s HA feature, we successfully re-started failed Exchange Server VMs on another XenServer host in less than three minutes. As soon as each re-started VM was recognized by Exchange, it immediately resumed taking on a workload. Other HA options include protecting storage and network connections using everRun VM from our alliance partner, Marathon Technologies. Another challenge solved.

This means we now have demonstrated perfomance when virtualizing Exchange Server 2007 with Citrix XenServer, and that performance comes with, and not at the expense of reliability, high availability and scalability. No trade-offs. No sacrificing one to get another.

It makes more sense than ever before for IT managers to take a serious look at the advantages of virtualizing Microsoft Exchange Server with Citrix XenServer. Check out the technical whitepaper and see for yourself. It contains extensive test configuration scenarios and results data along with recommendations and best practices so that anyone can easily configure and run their own pre-production pilot (highly recommended). And now that the Enterprise Edition of XenServer is available free of charge at, the cost to see the benefits of virtualizing your Exchange Server farm with XenServer yourself has never been lower. Don’t just take our word for it. It’s time to see for yourself.