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Virtual machines are wonderful things and server consolidation provides impressive and immediate ROI. However, server virtualization does not come without its challenges. According to Gartner, virtual machine (VM) “sprawl” is the number one concern when it comes to managing VM environments. Is this a valid concern? What does sprawl have to do with managing the life cycle of virtual machines?

This article looks at VM sprawl concerns and the role that effective Virtualization Lifecycle Management (VLM) plays in preventing it from occurring in IT environments.

What’s So Different About Virtual Servers?
Most virtual servers begin by viewing a virtual machine as similar to a physical one, but without the hardware cost. While this may be true at the beginning of a virtualized deployment, it quickly becomes clear that there are a number of significant differences between the two, making it easier to experience sprawl in the virtual world than in the physical one.

The first difference is subtle – identity. A physical server has a specific identity tied to its physicality that is usually attributed to the actual hardware. A VM on the other hand, is a great deal more ethereal. It is generated from a standard template that is cloned at the click of a mouse, producing many instances of the same server.

Another significant difference is mobility. Physical machines rarely move. Virtual machines, on the other hand, move a great deal, either through planned (or unplanned) maintenance, or through the agency of a growing number of software tools (e.g., load balancing tools that redistribute VMs based on host loads). VMs also tend to change state (e.g., powered on or off) more than their physical counterparts – another aspect of mobility.

The overall volume is another factor. A fully configured virtual server can be created in minutes, meaning many are easily generated, creating a different scale of management issues.

Finally, the life-cycle velocity is very different. VMs are created for many different reasons, some requiring a short life span while others require much longer. Consequently, the speed at which a VM moves through all the stages of its life cycle can range from minutes to years, while physical servers tend to be infinitely more predictable.

These differences create problems for traditional data center management tools that tend to be built for the “physical world.” VMs are counted more than once as they move through a short life cycle, or not counted at all if they cannot be seen (i.e., are offline or just not visible). This lack of visibility contributes to sprawl.

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