As computer hardware becomes increasingly more powerful, organizations are reaping huge cost and energy savings from replacing physical machines with virtual ones.
But whether you're replacing several physical servers with virtual machines running on a single host, streaming virtualized desktops to thin clients, or delivering virtual applications, if you don't balance the load on your resources your entire network can come screeching to a halt.
Think of load balancers as traffic cops, says Lew Smith, director of business development and virtualization solutions for consultant Interphase Systems. The devices keep the bits flowing smoothly to optimize performance, manage resources and ensure redundancy.
“Without load balancing, you'll get networking bottlenecks and reduced performance from apps,” says Smith. “It's like comparing a five-lane highway to a two-lane road. Both can handle the same number of cars, but the two-lane road will take a lot longer.”
Like the machines themselves, load balancing can be physical or virtual. Smith says most enterprises deploying virtualized environments use a combination of both: dedicated hardware appliances to manage data traffic coming in from the Internet or across internal networks, plus load balancing software to route data efficiently between physical layers and virtual ones.
Los Alamos National Laboratory uses VMware's Distributed Resource Scheduling to automatically spread the load across physical hosts in its virtual server environment.
“The primary benefit of DRS is management,” says Anil Karmel, a solutions architect for Los Alamos. “When we need to patch a node of the cluster, DRS dynamically moves the workload between hosts so we can push patches out without incurring any outage to the guests.”
While DRS can aggressively seek out resources as needed, Karmel says Los Alamos uses it in “balanced” mode. Thanks to early investments in capacity planning tools, the lab ensures sufficient resources for hosting its applications.
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“Capacity planning enabled us to deliver the right amount of resources to the virtual machines and achieve a high consolidation ratio,” he says. “Today, these same capacity planning tools continue to right size our platform, providing an agile, flexible and scalable offering to our user base.”
The U.S. House of Representatives reports lower operating costs, higher performance and greater network flexibility with its server virtualization project. And without proper load balancing, none of it would have been possible, says Jack Nichols, director of enterprise operations for the Office of the Chief Administrative Officer of the House.
Nichols says virtualization gives IT managers the ability to move individual virtual servers from one physical host platform to another (based on the aggregate loads of those host platforms) to balance out the applications so that one host is not saturated while another is lightly used.
“The ability to balance virtual servers across host platforms is absolutely a key benefit with virtualization,” he says. “It helps ensure performance expectations are met and provides valuable feedback to the organization on utilization trends of applications.”
More important, load balancing helps to ensure applications are available when users need them, even in the case of hardware failures.
“Every application owner I know believes his or her application is the most important application in the world and that any amount of downtime is too much,” he says.
In many IT environments, an application running on a physical server that fails could be down for hours before it's repaired. “In a virtual setting, if a host platform running multiple virtual servers encounters a hardware failure, those virtual servers can be moved to other virtual host platforms in a matter of minutes,” Nichols says.