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The hidden costs of virtualization, part 3: Licensing, performance and storage

This is part three of a three part article discussing the hidden costs that are associated with using virtualization in your environment.  The articles were written by David Marshall and Dan Knezevic, both of which have been using virtualization in the data center since 1999.  The articles come from years of hands on experience in many different environments. 

In part one, we discussed the power and heat costs and the management concerns of virtualization. Part two discussed networking issues and the problem of virtual machine sprawl. Finally, in part three, we will conclude by discussing licensing, performance and storage.

Licensing

Maintaining software licensing compliance is still another challenge. An administrator has a number of options in order to help maintain control over software licensing. But what happens to that control in a virtualized world? Physical restrictions are less of a deterrent in a virtual world with the use of ISO images and the ability to KVM into a virtual machine and control it all the way up front from the POST screen.

But perhaps the biggest problem facing IT administrators is the virtualization platform's ability to clone and replicate virtual machines. Without a method to control the mass duplication and deployment process of virtual machines, an administrator will have a license compliance issue nightmare on his hands.

Within a template or master image of a virtual machine lies a guest operating system as well as any pre-installed software applications, any or all of which may contain a software license and therefore a license restriction. An administrator needs the ability to keep track of how many instances of each image are deployed. If you thought maintaining control over licensing was a chore before virtualization, the problem has just been magnified.

Performance

One driving factor behind server virtualization is the need to increase the performance output of an under-utilized server. While it is true that server virtualization can more efficiently and effectively utilize the processing capacity of the server, what tends to get overlooked is the added stress that virtualization incurs on other physical resources. The disk subsystem may become an even bigger bottleneck to a system once the server consolidation process is completed.

The server's processor operates on an order of magnitude faster than that of a hard disk. So while server consolidation makes better use of the physical server's processor(s), it in turn slows down the performance of the disk I/O. As the number of virtual machines on a physical server increases, so does the number of guest operating systems that are each generating any number of disk I/O requests.

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Click here to read the entire article to find out more about performance and storage costs.

Published Monday, October 02, 2006 5:34 PM by David Marshall
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