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REDUNDANCY
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. n
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