N, N+1, 2N, 2N+1 Redundancy: What Do They Mean & Which Do You Need?

Evaluating the capabilities and infrastructure of data centers can be a confusing experience for many colocation customers. This is especially true when it comes to understanding data center redundancy, one of the most important aspects of any facility’s infrastructure. 

Data centers use specific terminology to describe a facility’s redundant systems including references to things like N+1 redundancy in specification sheets. In order to understand terms like “2N redundancy” or “N+1 UPS redundancy,” it’s good to consider why redundancy is so important in the first place.

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What Is Data Center Redundancy?

What Is Data Center Redundancy?

Redundancy is a critical component of IT infrastructure. It’s a practice and concept which establishes that systems should include either a component or full-system backup in the case said system fails, requires maintenance, or needs upgrades. In relation to data centers, redundancy is typically required for power supplies and cooling components as they are crucial for maintaining system health, accessibility, and reliability.

Read Also: How To Reduce Latency With Edge Computing And Network Optimization

Why Is Data Center Redundancy Important?

Redundancy is a major point of emphasis for data centers because a component failure can have serious consequences. When systems fail, data and services are no longer available to the companies and customers that rely upon them.

The impact is often felt within the organization when valuable human resources must be redirected to address the issue and productivity is impacted by the lack of access. Similarly, clients and potential customers are unable to access applications and data needed to complete transactions. Nearly everything comes to a standstill.
Not only is there a risk to accessibility, but redundancy also secures the data itself so that it’s protected from corruption and exposure to other vulnerabilities should any part of the system fail.

Finally, when considering the need to scale for business growth, redundancy ensures that, when installing new components, there is no downtime.  What’s at risk due to system failure and downtime goes well beyond lost revenue for clients and potential remuneration from service providers. It also represents missed business opportunities and potential damage to reputation that can tarnish a brand for years to come.

Understanding the Correlation Between Data Center Redundancy and SLA Uptime

For data centers and other service providers, their SLA uptime guarantee stipulates service expectations in terms of how much downtime customers can expect to experience over a period of time (usually a month). Routinely falling below that baseline not only costs the provider money in the form of remuneration payments, but it can also convince their customers to find a more reliable partner elsewhere. That makes data center redundancy incredibly important to most colocation facilities.

Types of Data Center Redundancy

What Does N Redundancy Mean?

The symbol “N” represents the infrastructure needed to operate a facility at full IT load. It is typically used to describe cooling units or uninterrupted power supplies (UPS), but it could apply to many other aspects of data center infrastructure. The important thing to remember is that N represents baseline capacity. A facility with N capacity has everything it needs to operate as designed, but it has no redundancies in place to accommodate equipment failure or maintenance.

What Does N+1 Redundancy Mean?

An N+1 redundancy means that a facility has the capacity needed to run a full IT load with an additional component to account for failure or maintenance. As a crude example, if four bolts were required to assemble a shelf from the hardware store, N+1 redundancy would supply five bolts. Datacenter N+1 redundancy standards typically require an extra unit for every four needed, so if 12 cooling units are required, a facility with N+1 redundancy would have 15 units.

redundant network

N vs. N+1 Redundancy: Understanding the Key Differences

It’s vital to understand that N is the baseline, which means capacity. It represents a system that is vulnerable to a single point of failure. If hardware breaks, something overheats, or power fails due to a storm or technical malfunction, the entire system goes down until the issue is addressed. As noted, this can come with significant business costs in terms of productivity and customer impact. Further, there could be a significant cost to replace or repair equipment as well as time spent trying to recover lost or corrupted data, if it can even be recovered.

As noted, N+1 ensures that there is at least one stage of backup on one, if not both, of those infrastructure components. While N leaves your system vulnerable to failures, N+ 1 means you’re at least covered in one area should hardware fail.

Small businesses, that don’t have 24/7 customer demand for services or goods, likely don’t need to make the investment in hardware to ensure redundancy. However, any business, medium-sized and larger,  relying on data and data accessibility should be utilizing, at a minimum, infrastructure with N+ 1 redundancy to ensure service accessibility and reliability. 

What Does 2N Redundancy Mean?

A 2N redundancy system is totally redundant, with a completely independent, mirrored system that can fully take over operational needs should the first system go offline for any reason. These systems are considered fault-tolerant because they can provide uninterrupted service even in the event of a significant failure to one system. Sometimes called N+N redundancy, 2N redundancy systems are easy to maintain because one system can be shut down for repairs or upkeep while the mirrored system continues to provide for the facility’s needs.

What Does 2N+1 Redundancy Mean?

The highest level of data center redundancy, 2N+1 redundancy provides a completely paralleled backup system along with additional components to account for failure and maintenance in each system. These systems offer tremendous versatility because they have full, fault-tolerant redundancy. Further, they have the ability to accommodate component failure without requiring a complete shift over to the backup system.

2N vs 2N+1 Redundancy: Understanding the Key Differences

With a 2N system, a failure should trigger movement over to the secondary independent mirrored system while issues in the first system are addressed. However, what happens if there’s an additional failure?

If we look at mirrored systems in the body, we can consider our arms or legs. These are symmetrical systems that work independently of one another but have the same function – mobility. If you sprain an ankle or break one leg, you’re still mobile. The secondary system steps in to perform the function. That is, you can get around and work around the injury. However, if there’s an injury to the second leg, suddenly the system doesn’t work anymore; your mobility would be severely limited without some other kind of backup or support. That’s where the +1 in 2N+ 1 becomes a vital part of this level of redundancy.

With 2N+ 1, not only do you have the secondary system to fall back on but if something should fail within either system, it’s also backed up, meaning you have a crutch. In other words, it would take something catastrophic to take down the entire system, and most issues can be resolved without ever relying on a full transfer. This option is largely required by multi-million dollar businesses that require 100% uptime and will face significant financial and future losses if their system were to crash.

Which Type of Data Center Redundancy Is Right for Your Business?

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Selecting the appropriate level of redundancy can be a difficult decision for an organization. While it might be tempting to want the highest level of redundancy, not every industry calls for the same uptime and availability standards. For most companies, N+1 redundancy is a good baseline that balances high reliability with affordable colocation costs. Full 2N redundancy is often quite expensive to install and maintain. As a result, some organizations could end up paying more for redundancy they just don’t need.

Still, data center redundancy is an important consideration that companies should never take for granted when evaluating potential colocation partners. Understanding how data centers assess redundancy is a good starting point for evaluating the capabilities of a specific facility. Given the risks associated with system downtime, organizations can’t afford to overlook their data center’s redundant systems. With N+ 1 redundancy, your business will get the uptime it needs, ensuring both accessibility and reliability.

Ruben Harutyunyan

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