5 Ways Not to Use Virtualization

March 3rd, 2010 by Andrew H.

With all of the talk about virtualization lately, many organizations are ready to pick up everything and virtualize it. After all, it’s the thing to do! Here are some things to keep in mind before virtualizing everything in sight:

1. Don’t virtualize highly utilized servers

One of the biggest benefits of virtualization is being able to make better use of your hardware. Adding virtualization doesn’t add more horsepower to your server; in fact, it’s another layer that can reduce performance. If you have a service that is already using most of the resources on a fairly powerful server, there’s a good chance that it might not be the best candidate for virtualization. If you decide to virtualize a workload that is disk intensive, consider using a raw pass through disk instead of a virtual hard disk to improve disk I/O performance.

2. Don’t cluster a cluster

Many virtualization platforms allow you to provide for some level of high availability for your VMs. Applications can provide a similar feature, but use caution when using them together. Generally speaking, services clustered with Microsoft Cluster Services that use a shared disk should never be configured in a way that makes the virtual machines automatically move from one server to another. Having multiple levels of failover might cause unexpected results and unnecessary disruptions to users.

3. Don’t virtualize everyone’s desktop (and expect to save money)

There are some legitimate benefits to virtualizing desktops, but cost is usually not one of them. No matter where a desktop is, users still need something to access it with. Server hardware is also inherently more expensive than traditional desktop hardware. On the other hand, virtualized desktops can be a great fit for remote employees, as backup workstations, or to ensure standardized desktops. In most cases, however, a Remote Desktop Services session host (previously Terminal Services and available only on Windows machines) can provide a cheaper and more efficient alternative provided that users don’t require administrative privileges.

4. Don’t create conflicting dependencies

Virtualization platforms can rely on a variety of services– Active Directory, management software, DNS, and a variety of others. Before you virtualize something, make sure your virtualization hosts can function correctly without those services running– after all, you can’t start the VMs before the host! For management software such as vCenter or SCVMM, check the product documentation to see when (if ever) they can virtualized on the same servers they are managing.

5. Don’t virtualize applications that require very accurate time

Time isn’t kept in a virtualized environment the same way it is on a physical host. Because VMs are much more prone to “time drift”, most virtualization platforms include time synchronization when the appropriate integration components are installed. Even with these time synchronization components, it is still more likely to encounter time drift on a VM than a physical host.

Like every piece of technology, though, virtualization does have its place. I hope this list will really help you decide if it’s the right decision for you, or at least help in your virtualization endeavors!