Four mistakes that can kill virtual machine performance

Screensavers, managing from the console, real-time security scans and certain Windows Server power options can all undermine virtual machine performance. Here's how to avoid VM performance killers.

Ah, how I love the easy ones. In many cases, the easiest mistakes cause some of the biggest performance problems...

in virtualization environments. In my consulting, I've seen a few major errors that are worth sharing. Some of these may seem obvious, but consider checking your settings. You may be surprised at what you find.

Easy Mistake 1: Virtual machine screensavers

Screensavers are an absolute requirement for desktops in the hallways of our brick-and-mortar offices. They ensure that a user who walks away from his computer returns to one that has been secured against prying eyes. Screensavers can also provide protection in data centers. If screensavers on servers activate and lock the console after a few minutes of inactivity, they can protect that environment from an intruder who gains physical access.

But screensavers are a quiet consumer of processor resources. No matter how insignificant that screensaver seems, the processor power required to draw the pipes crawling across the screen or to scroll your favorite company slogan consume a percentage points of overall processor power. While that might not seem like much, consolidated virtual environments might have 10 or 15 virtual machines (VMs) running on a single virtual host. These percentage points add up when they are multiplied by the number of VMs. Even worse, if your environment uses hosted desktops through a virtual desktop implementation, this practice likely costs even more.

So turn them off. Remember that many environments enforce screensavers through group policies, which may mean an exclusion from existing group and corporate security policies.

Easy Mistake 2: Managing from the console

This second mistake is one of my favorites, because it is common among IT administrators everywhere. Do you manage your infrastructure components by remoting and logging into their individual servers? Do you run the Exchange Management Console from your Exchange server? Do you check domain name server (DNS) settings from the server's console? Do you manage Active Directory by remoting your domain controllers?

If you are, stop.

As with screensavers, this practice is a big no-no in virtualized environments because of the level of resources required to create and maintain an instance of the Explorer shell. Just logging into a virtual machine is hard on that VM's processor utilization. The process of creating a shell for the console can spike processor utilization during the login and logout process. Actually using any of the consoles on that server further consumes valuable resources. Logging in and accomplishing activity on your VMs' desktops increases the amount of memory they consume.

Microsoft provides the Remote Systems Administration Toolkit, PowerShell and VBScript, as well as many other tools for efficient virtual machine management. All these lightweight tools require much less VM capacity than a traditional login. So use them, and avoid wasting processing power and memory like an amateur.

Easy Mistake 3: Antivirus and anti-malware scanning of VM disk files

Your corporate security policy might not allow for the exclusion of Virtual Hard Disk or Virtual Machine Disk Format (VMDK) files from antivirus and anti-malware scans. But be aware that the real-time scans of such products can substantially reduce the overall performance of these files -- and, thus, their virtual machines. Since a VM's processing is highly dependent on its disk subsystem, any extra activities that slow down that process slow it down as well.

That's not to say that VM disk files shouldn't be subject to security scanning. Scheduled scans of such files can ensure that they don't get infected, without the processing overhead of real-time scans. Also, some of today's more advanced scanning products are beginning to incorporate virtualization awareness to reduce their overall impact. If your security policy will allow it -- or if you can bribe your security officer to look the other way -- definitely consider excluding these files from your real-time scans.

Easy Mistake 4: Windows Server's power options

At conferences around the country, I've encountered the final mistake repeatedly. The default power option of Windows Server 2008 upon installation is set to "Balanced." Of the three options available -- Balanced, Power Saver and High-Performance -- this is the second of the three in terms of overall system performance. You might save a few dollars on energy, but at the cost of wasting some of the server's processing power. Resetting the radio button to the high-performance option has a noticeable effect on how well VMs will perform.

Group policy is probably the easiest way to do so. If you create a new policy and navigate to "Computer Configuration > Policies > Administrative Templates > System > Power Management," look for the policy called "Select an Active Power Plan." Configuring this policy across your server infrastructure ensures that you always run with highest performance.

If you've got an easy mistake that I've missed, I've love to hear about it. Drop by www.concentratedtech.com and tell me about your own fixes for easy virtualization mistakes!

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.

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