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Server virtualization myths and realities exposed

It saves money. It doesn't save money. It cuts staff. It adds staff. What's the truth behind common vendor claims about server virtualization? One expert has the answers.

Server virtualization is the technology du jour, but there is much debate about what it can really do in a corporate enterprise. David Payne, chief technology officer at Xcedex, an integration company based in Bloomington, Minn., specializes in helping companies develop and implement strategies. Payne recently outlined his general rules of thumb with Margie Semilof, news director at

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I'm sure plenty of IT managers think they can reduce their staff count by virtualizing their servers. Do staff sizes shrink if the hardware consolidates?

David Payne: This is a common [misconception]. Unless you are spending a lot of time doing hardware management, in the shops we've worked, we haven't seen massive staff reductions. One of the most common practices today [with server virtualization] is server consolidation. You are reducing the number of physical servers but increasing the number of [operating systems] on each server.

There is a lot of expectation that server virtualization equals big cost savings. How true is that?

Payne: There is quite a bit of cash to be saved. The cost of virtualization keeps going down, but it's still not free. Look at the associated costs. And some shops want to bring up virtual machines almost in an outrageous fashion.

In one case, a client got a virtual environment up, and in one of the applications people said they wanted 10 virtual machines. They wanted to do a software development life cycle from development to test to quality assurance to production.

Virtual machines are not free. There is a Windows license. [They] do require server resources. You have to buy the box. A virtual machine costs about one-third of a physical machine.

There is also ongoing maintenance comparable to any application you bring online. There is yearly maintenance. You've got to maintain the OS. You have to retrain people to support these new applications.

Which applications cannot be easily virtualized?

Payne: The blanket statement that you can virtualize everything is inaccurate. There are different virtualization packages. There is VMware with ESX Server, Microsoft Virtual Server, SWSoft, Xen and Virtual Iron. They are all similar but have different performance capabilities and claims.

Not all platforms support [virtualization]. We look at the size of the container of the virtual machine. We look at what kind of applications can be virtualized. You are limited by the size of the virtual machine you can create. You might be able to install ESX on a big server, but the virtual machine capability is limited to the size of its container.

[Microsoft's] SQL Server chews up too much computing power. Heavy disk I/O can't be forced into a virtual machine box. A virtual machine can't handle the load even though the host can handle it. With Exchange, it comes down to the database behind Exchange. It too is I/O-intensive.

These things are changing. It tends to be costly to virtualize those parts of the computer, and in the end, performance isn't good. But the new version of ESX Server has doubled the size of the container. There has been lots of optimization in the network stack, and the hardware guys are catching up as well. Intel, IBM and HP are [designing] their hardware platforms.

Virtualization is a killer app that will drive hardware to its limits. [Hardware vendors] are building virtualization into the chips. Multi-core's are out. Dual cores. They are very virtualization-friendly. And [Intel's] VT and [AMD's] Pacifica are taking the software processing right down to the silicon, which will bring huge performance increases.

How about the claim that virtualization eliminates downtime?

Payne: VMware likes to talk about how it eliminates downtime. This is not quite so true. Its VMotion [software that lets IT shops move live virtual machines from one host server to another while running continuously] is great, and it does eliminate planned outages. But VMotion doesn't help patch. It can't. I have to reboot my guest OS when patches are applied so VMotion doesn't eliminate all outages all together. It doesn't eliminate weekends. You still have to do reboots.

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