Virtualization's downsides

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Despite virtualization's well-known benefits, problems can crop up.

Andi Mann, senior analyst with Enterprise Management Associates, an IT consultancy based in Boulder, Colo., says that virtualization's problems can include cost accounting (measurement, allocation, license compliance); human issues (politics, skills, training); vendor support (lack of license flexibility); management complexity; security (new threats and penetrations, lack of controls); and image and license proliferation.

Mann says that enterprises sometimes have difficulty finding or applying adequate monitoring and management tools that work across both virtual and physical landscapes. Other issues can include support, integration and compatibility of different operating systems on the multivendor hardware being virtualized.

Increased uptime requirements arise when enterprises stack multiple workloads onto a single server, making it even more essential to keep the server running. "The entire environment becomes as critical as the most critical application running on it," Mann explains. "It is also more difficult to schedule downtime for maintenance, because you need to find a window that's acceptable for all workloads, so uptime requirements become much higher."

Bandwidth problems are also a challenge, Mann says, and are caused by co-locating multiple workloads onto a single system with one network path. In a physical server environment, each application runs on a separate box with a dedicated network interface card (NIC), Mann explains. But in a virtual environment, multiple workloads share a single NIC, and possibly one router or switch as well.

This setup can increase the network traffic through this single path, "resulting in problems with bandwidth availability and throughput," Mann says. Besides these technical concerns, enterprises also must often deal with misleading and conflicting vendor claims, plus the potentially unexpected costs of additional hardware and software for a virtualized environment, Mann adds.

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