Redundancy. What the heck does N+1 mean?

Written by Joe Kozlowicz on Wednesday, December 12th 2012 — Categories: Green Data Center, FAQs

At its most basic definition, N+1 simply means that there is a power backup in place should any single system component fail. The ‘N’ in this equation stands for the number of components necessary to run your system. The ‘+1’ means there is one independent backup should a component of that system fail.

To help you understand, I’ll give you a little scenario. Say you have a family of three, two parents and one kid. All three family members drive, and all three have cars. But, you also have one extra car, in the case of one of the regular three breaking down. So the three cars is the ‘N’ – the amount needed to keep your family running smoothly. The ‘+1’ is the backup for that. Make sense?

Now, there is a level of redundancy called 2N. In that instance, you have a duplicated component for every single component. In the car scenario, there would be three extra cars (six total), one specifically for each vehicle. As you can imagine, that system is incredibly wasteful.

At Green House Data, we actually have a bit of a mixed system that is referred to as concurrently maintainable. In words more succinct than my own: “Very simply, it means that anything in your data center can be shut down and kept down for a period of time, without directly affecting ongoing processing…If everything has been well maintained, the statistical chance of a simultaneous failure practically drops off the charts. Further, to actually bring down a facility that is designed and installed for concurrent maintainability most likely takes not two, but at least three sequential events.” (source)

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Based on this reasoning, you can see why chose a concurrently maintainable system, with minimal waste, versus a 2N redundancy, in which nearly half of your equipment is simply wasted.

Practically, all of this is to say that you will never experience a power failure at Green House Data – hence our 100% SLA. Well, I suppose we can’t say never. If, per chance, we encounter a large meteor strike AND a zombie attack on our power grid AND a rogue invasion of ninjas all AT THE SAME TIME, then there might be a power failure. Crossing our fingers!


n+1 redundancy

With our cloud infrastructure, we even have this redundancy at the data center level, as we have three facilities. Should one, or even two data centers suffer catastrophic failure, we remain operational. How’s that for redundancy?

If you have remaining questions about power redundancy, feel free to contact us. We'd be happy to talk more about this and other questions you may have.