Why might someone use an N+1 approach for a cluster?

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N+1 or N+1 redundancy is a popular concept in network virtualization and the design of IT architectures. Companies generally use this design to provide effective backup or ensure smooth system operation with a single point of failure.

The name “N+1” signifies a process by which engineers include a range of functioning nodes in a cluster, and then add one extra, so that if there is a single point of failure, that one extra unit can stand in the gap. This process can also be called “active/passive” or “standby” redundancy.

Companies use an N+1 design to make sure that if one server or virtual machine fails, the system is not impacted. However, a greater discussion has emerged about whether N+1 redundancy is sufficient for a given system. There is the recommendation against trying to provide a one-size-fits-all approach when providing redundancy for high availability. IT pros also understand that the stricter a client is with high availability requirements, the more redundancy is needed.

In response to this philosophy, engineers have provided things like N+X+Y, in which many more resources are added to the system to make sure that even a multipoint failure doesn’t impact operations. Another particular consideration is the size of each virtual machine or node in the cluster – for example, if a single VM is 100 GB and the others are under 50 GB, an N+1 approach would not ensure functionality if that larger VM is compromised.

In general, N+1 is simply a tool and an approach to managing resources like CPU and memory across any shared environment such as a network cluster. It is evaluated for its effectiveness and efficacy in a particular IT system depending on resource allocation and the overall setup.

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Justin Stoltzfus
Justin Stoltzfus

Justin Stoltzfus is an independent blogger and business consultant assisting a range of businesses in developing media solutions for new campaigns and ongoing operations. He is a graduate of James Madison University.Stoltzfus spent several years as a staffer at the Intelligencer Journal in Lancaster, Penn., before the merger of the city’s two daily newspapers in 2007. He also reported for the twin weekly newspapers in the area, the Ephrata Review and the Lititz Record.More recently, he has cultivated connections with various companies as an independent consultant, writer and trainer, collecting bylines in print and Web publications, and establishing a reputation…