Virtualization's dirty little secrets

The server virtualization drum beat gets louder with Microsoft poised to enter the market, but adoption pitfalls could lead to a bad user experience.

 

A small company also may not have the necessary SAN expertise or, for instance, capability to mesh Cisco switches and VMware's complex virtual networking stack. "Virtualization draws together so many different aspects of networking, server configuration, and storage configuration that it requires a well-seasoned jack-of-all-trades to implement successfully in a small environment," Prigge wrote in a "virtual" case study for the Test Center that’s chock full of insight about challenges ranging from pricing and products to technical and skills requirements.

Larger companies don't have it easier, either. Getting a lot of people in disparate teams -- server, storage, business continuity, security -- on the same page is a feat, especially since they traditionally don't talk to each other very much. All of them, though, need to be educated about virtualization. If there's a problem with an application, for instance, an administrator must know where virtual machines exist throughout the server farm so that he doesn't reboot a server and unwittingly take down all the virtual machines on it.

Gotcha No. 3: Performance boosts aren't always what they're cracked up to be
Despite the hard work, virtualization adopters may feel a sting of disappointment. Many will have embraced server virtualization with grand expectations, only to see performance fall short. Burton Group's Wolf points the finger at vendors: "For me, the way VMware advertises performance benchmarks is completely inaccurate."

The vendor publicity materials' virtual machine benchmarks involve running a single virtual machine on a single physical host. But a typical production environment is conservatively eight to 12 virtual machines per physical host. "This paints an overly optimistic picture of performance," Wolf adds. "They also tend to gloss over things like over-allocation of CPU cores" that can tax the hypervisor's CPU scheduler and lower performance.

Memory is another big performance-buster, Wolf says, especially with virtualizing multithreaded applications. When separate threads within an operating system continually try to refresh memory, the hypervisor's shadow page tables get backed up. The result: latency. For applications that rely heavily on memory, latency spikes and application responsiveness deteriorates. Users may start seeing connection timeouts.

"Hardware-assisted memory is one solution, but it's also a crap shoot," Wolf says. "Some applications run better with hardware-assisted memory virtualization while others run better with shadow page tables."

The fallout of lackluster performance can be huge. A company might have to fork out more cash for servers. Business execs may demand that applications be given their own servers again. "Restoring trust in virtualization technology, it may take a couple of years before a company attempts to virtualize again," Wolf says.

And there are even more gotchas to avoid
Poor performance, unprepared staff, and hidden costs are only a sampling of the pitfalls in server-virtualization adoption. Managing the whereabouts of virtual machines can be a nightmare, given that they can be moved from one physical server to another, or even walk out the door on a portable hard disk. Security risks abound, too. Audit failures due to the lack of full separation of security zones can happen more easily in a virtual environment.

And then there's the threat of virtual server sprawl; new applications are easy to get up and running in a virtual world. "Virtualization increases your appetite for software," IDC's Humphreys says. "One company went from 1,000 applications to almost 1,300." Not only are there potential software licensing costs involved but also the task of tagging and tracking the applications.

Of course, server virtualization's plethora of pitfalls won't stop people from adopting the technology. After all, the benefits in a good implementation can be tremendous. But knowing how to identify and avoid those gotchas can make the journey more pleasant and the reward that much sweeter. "There's no slowing virtualization down; the benefits are too great," Dineley says. "But you will get buried if you don't steer clear of the gotchas."

Tom Kaneshige is a senior writer at InfoWorld. He can be reached at tom_kaneshige@infoworld.com.