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How to evaluate high availability options for virtualized IT environments

John Moore | April 30, 2013
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.

Lin says VMware HA calls for an n+1 design to ensure sufficient resources for failover or server maintenance. A two-host cluster, for instance, should not exceed the CPU and memory performance of one host. In that case, 50 percent of cluster resources would be reserved for failover.

A cluster with more hosts offers higher utilization and diminishes the impact of a host failing, Lin notes. A four-host cluster, for instance, would reserve 25 percent of its resources for failover.

Christian Teeft, vice president of engineering at Latisys, said solutions such as VMware HA are a good fit for customers who seek availability but can tolerate a brief interruption while workloads are reloaded and started on another server. Latisys, a multi-tenant data center company, builds availability into its solutions.

Teeft said some customers-those with big data analytics applications, for example-may run hundreds of virtual machines for number crunching, and the loss of a node in the cluster won't severely impact overall performance. For organizations with that profile, Latisys builds data center solutions around VMware HA and the Hewlett-Packard Converged Infrastructure platform, Teeft notes.

SQL server clusters provide more uptime, more to manage

Customers, however, can move beyond VMware HA for more protection. Lin suggests that customers could look into an additional cluster for a specific application such as SQL Server.

A cluster, in this scenario, would consist of an active node running a SQL Server database and a passive node on standby. The passive node starts SQL Server when the active node fails. Customers can use Microsoft clustering technology or third-party software such as Vision Solutions' Double-Take Availability, Lin says.

A cluster specific to SQL Server will provide more uptime than what VMware offers out of the box, Lin says. Clusters of this kind are more tightly integrated with the application itself, he adds, whereas VMware HA "has no idea what application you're running."

The drawbacks to this option, Lin says, include the creation of another cluster that customers must manage. If a third-party product is used, there's also the complexity of an additional piece of software.

Several other vendors have high availability clustering offerings. These include Dell, Enhance Technology, Hewlett-Packard, IBM, Intel and Proxmox.


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