How to Evaluate High Availability Options for Virtualized IT Environments

One upside to virtualization is that it puts more applications on fewer servers. One downside is that the availability of those servers become of greater importance.

By John Moore
Mon, April 29, 2013

CIO — As virtualization puts more application eggs into fewer server baskets, design principles such as high availability require more attention.

Consultants and IT managers working in the virtualization field say enterprises take a variety of approaches to keeping their apps online. Many use high availability software associated with the widely used VMware hypervisor. Various forms of clustering also aim to minimize downtime. Efforts to boost the reliability of physical hardware are also underway.

More Apps, Fewer Servers Equals Demand for High Availability

The high availability and fault tolerance revivals stem from a couple of factors, among them the greater concentration of applications on consolidated servers. "If you add enough non-mission critical application to the same server, it makes it mission critical," says Nigel Dessau, chief marketing officer at Stratus.

Overall, continuous availability has become much more important in the cloud era compared with the days of client/server, Dessau contends. Back then, fat clients shared more of the workload, so users could keep working on their PCs in the event of a server crash. Apps that couldn't afford downtime were backed by fault tolerant servers, which Dessau says only represented perhaps 5 percent of the market.

News: Stratus Acquires Competing HA Software Provider Marathon

The market reach of availability technology may grow amid virtualization and cloud computing, however. "In the cloud world, you have thin clients or even mobile devices," Dessau says. "In this case, when the server is not available, [users] become severely limited as to what they can do. The server's availability is much more essential."

Kris Lamberth, chief technology officer at Paranet Solutions, a Dallas-based CRM and IT outsourcing company that offers virtualization services, notes that customers are becoming increasingly aware of the cost of downtime. "I think everybody is looking for high availability today just because everyone is so dependent on IT," he says.

An enterprise's actual investment in availability ultimately depends on the importance of a given application—and how eager the firm is to pay for uptime.

VMware High Availability Approach Focuses on Clusters

Availability options for virtualized customers often start at the hypervisor level. The VMware vSphere High Availability feature, for example, checks the health of virtual machines and detects problems.

If an operating system failure is detected, VMware HA automatically restarts the virtual machine. If a virtual machine's underlying physical server fails, VMware restarts the application on another server. (A cluster of vSphere ESXi hosts makes that failover possible.)

Milton Lin, master cloud specialist at Force 3, a Crofton, Md.-based systems integrator, says VMware tends to be the hypervisor of choice among Force 3clients due to its simple availability approach. "For any VMware administrator or environment with VMware already, VMware HA is easy."

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