2N vs N+1

By Okey Keke, Senior Solution Architect, Digital Realty www.digitalrealty.co.uk

Keeping data centres online in the event of the unexpected

The only certainty is uncertainty. From powerful storms to unexpected power outages, you never know what life is going to throw your way, or towards your data centre. That’s why redundancy is your IT environment’s best friend when the unexpected happens.

What is redundancy?
Redundancy refers to a system design where a component is duplicated so that in the event of a component failure, IT equipment is not impacted. The main goal of redundancy is to ensure zero downtime.

Redundancy Lingo
You may have seen terms like 2N and N+1. But what do these actually mean? The term ‘N’ simply represents the unit that you wish to duplicate – whether it’s a generator, UPS, or cooling unit. N equals the amount of capacity required to power, backup or cool a facility at full IT load. A design of N means the facility was designed only to account for the facility at full load and zero redundancy has been added. If the facility is at full load and there’s a component failure or required maintenance, mission-critical applications would suffer.
If N equals the amount of capacity needed to run the facility, N+1 indicates an additional component added to support a single failure or required maintenance on a component. Design standards typically call for one extra unit for every four needed. So, if you have, say, eight UPS units, then you should at least have 10 total UPS units.
2N refers to a fully redundant, mirrored system with two independent distribution systems. They aren’t connected in any way and aren’t dependent on each other. This means that even if one power source has an interruption or loss of power, the other should still supply power and accommodate full load, thereby eliminating any potential downtime from the loss of one side or leg of the system.

Why is redundancy needed?
When your applications crash unexpectedly, this can have a serious and direct impact on your organisation’s bottom line, business operations, and customer experience. According to an annual survey conducted by the Information Technology Industry Council (ITIC), 98% of organisations say that a single hour of downtime costs over $100,000. Beyond dollar signs, downtime can severely impact the productivity of your workforce when they’re tied up with frantically trying to get back online instead of focusing on other core focus areas for your business.
At the end of the day, there’s no way to completely prevent things like natural disasters, local grid failures or power outages, so it’s crucial for every organisation to be prepared for when – not if – redundancy is needed.

What’s the right configuration for you?
There’s no right or wrong redundancy configuration since it depends on many factors like your IT environment, business goals, and budget. It’s always best to have this discussion with your account rep, sales engineer and solution architect to figure out the best option for you.

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