What Is Data Center Redundancy? N, N+1 and 2N+1 Explained

Data Center Redundancy Explained
Data Center Redundancy Explained

What is a Data Center?

A data center is a modern, hi-tech building which offers multiple services and features.

These could be co location, disaster recovery services, business continuity, dedicated server hosting etc.

What is a Data Center Tier Certification?

A tier certification is a measure of an enterprise data center provider’s standards.

The most basic parameters inspected are quality of service, redundancy and security.

There could be more criteria based on which a tier certificate could be issued.

Fundamental Principles of the Tier System

The data center tier or rated certification is regulated by the principles of the Uptime Institute – the premier organization which determines the tier rating system and provides a tier certificate to every enterprise data center, colocation data center and data colocation service provider.

The guiding principles followed by the Uptime Institute in their own words are:

Elasticity – The performance-based nature of the Tier standards gives organizations flexibility to comply with local statutes, codes, and regulations while enjoying full Tier certification and the business benefits of doing so.

No technology bias – In an ever-changing technology landscape, Tier classification does not require or rely on any fixed set of technologies. The Standards are able to encompass new and innovative solutions for data center systems and engineering.

Service and performance centered – Tier Standards have been created based on the expected service levels from a co location provider or an enterprise data center. Any design solution that meets the requirements for availability, redundancy, and fault tolerance is acceptable.

Any data center – be it a co location service, data colocation offering or an enterprise data center hosting a dedicated server; is classified on their service quality and ability based on their tier or rated certificate.

What Is Data Center Redundancy?

An enterprise data center designs their systems and equipment in such a way that every section of its infrastructure (power, cooling and network) has an active backup available to cover failures.

Redundancy is designed into systems and components to achieve zero downtime or near zero service disruption at all times.

These are very important to achieve, especially for co location providers.

What is “N”, “N+1” and “2N+1” in Data Center Redundancy? 

These three terms are used to measure an enterprise data center’s infrastructure design.

N Redundancy

“N” – It is simply a count of the equipment, tools, services and components required for a data center to function.

If an enterprise data center is designed with only “N” in mind, it means there is no redundancy available in case of a failure.

A colocation data center should never be in such a state.

N+1 Redundancy

“N+1” – Since “N” is the count of all tools and equipment needed to support an enterprise data center at its full load, “N+1” is the presence of an additional setup being available in a colocation data center or data colocation service place.

An enterprise data center is said to be a “N+1” facility when it has 1 backup unit or equipment for every 4 pieces of the same component in production service.

For example – if a co location provider uses 8 power supply units for electricity supply on a floor, they should have at least another 2 units in spare.

2N+1 Redundancy

“2N+1” – A co location provider is deemed to be at a 2N+1 redundancy when the data center design has two full set of equipment, services and tools which might be needed to run an enterprise data center.

For example – if a data colocation provider or a server colocation provider run their services with 4 network links, they would have another 4 links which act like a backup if something goes wrong with the first set.

It means they have a secondary set of equipment and tool ready to take over if something happens to the production units to ensure zero downtime to customers.

What is the Difference in the Different Ratings of a Data Center?

All enterprise data centers in the world are rated between Tier 1 to Tier 4 (or Rated 1 to Rated 4).

Those providing co location service take pride in their data center’s tier ratings as it showcases their redundancy and uptime.

Tier 1 Data Center (Basic Capacity)

It is the lowest-rated tier but is above putting a stack of servers in a closet in the office.

The performance of this tier is at the lowest of all tiers with an uptime of 99.671%.

This tier lacks IT equipment that supports redundancy. These are not termed as enterprise data center facilities.

A Tier 1 data center work best for very small businesses looking for an affordable option.

There can be up to 1729 minutes of annual downtime.

Tier 2 Data Center (Redundant Capacity Components)

It is the 2nd lowest-rated tier. These data center facilities offer the capabilities of Tier 1 and offer additional fail-safes for backup that includes UPS modules, chillers, pumps, and energy generators

A Tier 2 data center is commonly used by small businesses that want a cost-effective option and can live with downtime.

They offer a marginally higher uptime of 99.741%, which translates to no more than 1361 minutes a year.

Such a data center cannot offer co location as a service.

Tier 3 Data Center (Comprehensive Redundancy)

A Rated 3 or Tier 3 data center can be called a co location facility or data colocation provider.

These buildings come with an additional redundant path for backup which kicks in in the event of a failure.

A Tier 3 enterprise data center or a co location provider restricts their annual down time to a maximum of 95 minutes a year.

Tier 4 Data Center (Fault Tolerant)

A Rated 4 or Tier 4 data center is the most secure, robust and reliable form of an enterprise data center.

Be it co location, server colocation or dedicated server plans – any web hosting service can be easily and safely run from such a facility.

The strictest of all design guidelines ensures an identical replica being available for every component with an enterprise data center.

When someone asks what is a data center, the answer would be “a facility which is fault tolerant”.

A Tier 4 enterprise data center comes with an uptime of 99.995%, meaning annual downtime of no more than 26 minutes.

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