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.

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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.

Frequently Asked Questions

Q: What is N+1 redundancy and how does it work?

A: N+1 redundancy is a type of system design in which there is one more redundant component than is strictly necessary to perform a given function. For example, in an N+1 redundant system with three components, only two of the components are needed to perform the required function, but a third component is included as a standby in case one of the other components fails.

In an N+1 redundant system, the extra component is typically used in a standby or hot standby configuration, meaning that it is not actively in use but is ready to take over if one of the other components fails. When a failure occurs, the standby component is brought online to take over the functions of the failed component. This allows the system to continue operating without interruption, even if a component fails.

The advantage of N+1 redundancy is that it provides a high level of reliability and availability, as the system can continue to operate even if a single component fails. It is commonly used in mission-critical systems where downtime or failure is unacceptable, such as in power plants, data centers, and other critical infrastructure.

Q: How does 2N redundancy differ from N+1 redundancy?

A: 2N redundancy is a type of system design in which there are twice as many redundant components as are strictly necessary to perform a given function. For example, in a 2N redundant system with six components, only three of the components are needed to perform the required function, but six components are included in the total, with three in active use and three in standby.

In a 2N redundant system, the extra components are typically used in a hot standby configuration, meaning that they are not actively in use but are ready to take over if one of the other components fails. When a failure occurs, the standby component is brought online to take over the functions of the failed component. This allows the system to continue operating without interruption, even if a component fails.

The advantage of 2N redundancy is that it provides an even higher level of reliability and availability than N+1 redundancy, as the system can continue to operate even if two components fail. It is commonly used in mission-critical systems where downtime or failure is unacceptable, such as in power plants, data centers, and other critical infrastructure.

One key difference between N+1 and 2N redundancy is the number of components that are included in the system. In an N+1 redundant system, there is one extra component, while in a 2N redundant system, there are twice as many components as are strictly necessary to perform the required function. This means that 2N redundancy is more expensive to implement and maintain than N+1 redundancy, but it also provides a higher level of reliability and availability.

Q: What are the benefits of using N+1 or 2N redundancy in a system?

A: There are several benefits to using N+1 or 2N redundancy in a system:

  1. High reliability: By including extra redundant components in the system, N+1 and 2N redundancy can increase the reliability of the system, as it can continue to operate even if one or more components fail.
  2. High availability: N+1 and 2N redundancy can also increase the availability of the system, as the extra components can be brought online quickly to take over the functions of a failed component, minimizing downtime.
  3. Improved performance: In some cases, using N+1 or 2N redundancy can improve the performance of the system, as the extra components can be used to distribute the workload and increase capacity.
  4. Increased resilience: N+1 and 2N redundancy can also increase the resilience of the system, as it can continue to operate in the face of component failures or other disruptions.
  5. Cost-effective: While N+1 and 2N redundancy can be more expensive to implement and maintain than some other types of redundancy, it can be cost-effective in the long run, as it can minimize the need for costly repairs and downtime.

Overall, the main benefit of using N+1 or 2N redundancy is that it can increase the reliability, availability, and resilience of a system, making it more suitable for mission-critical applications where downtime or failure is not acceptable.

Q: How do you calculate the required number of redundant components for N+1 or 2N redundancy?

A: To calculate the required number of redundant components for N+1 redundancy, you will need to know the number of components that are required to perform the desired function (N). The formula for calculating the required number of redundant components for N+1 redundancy is as follows:

Number of redundant components = N + 1

For example, if you need three components to perform a given function, you would need three + 1 = four redundant components to implement N+1 redundancy.

To calculate the required number of redundant components for 2N redundancy, you will again need to know the number of components that are required to perform the desired function (N). The formula for calculating the required number of redundant components for 2N redundancy is as follows:

Number of redundant components = 2 * N

For example, if you need three components to perform a given function, you would need 2 * 3 = six redundant components to implement 2N redundancy.

It’s worth noting that these formulas assume that the redundant components are used in a hot standby configuration, meaning that they are not actively in use but are ready to take over if one of the other components fails. In other configurations, such as active/active or active/passive, the number of redundant components may need to be adjusted.

Q: In what types of systems is N+1 or 2N redundancy commonly used?

A: They are commonly used in a variety of systems where high reliability and availability are important, including:

  1. Power systems: N+1 and 2N redundancy are commonly used in power systems, such as power plants and electrical grids, to ensure that there is always a backup source of power available if one component fails.
  2. Data centers: N+1 and 2N redundancy are also commonly used in data centers to ensure that critical data and services are always available, even if a server or other component fails.
  3. Communication systems: N+1 and 2N redundancy are often used in communication systems, such as telephone networks and satellite systems, to ensure that there is always an alternative means of communication available if one component fails.
  4. Industrial systems: N+1 and 2N redundancy are also commonly used in industrial systems, such as manufacturing and process control systems, to ensure that the system can continue to operate even if a component fails.
  5. Military systems: N+1 and 2N redundancy are frequently used in military systems, such as aircraft and weapons systems, to ensure that they can continue to function even if a component fails.

Overall, N+1 and 2N redundancy are used in a wide range of systems where high reliability and availability are important, including critical infrastructure, data centers, communication systems, industrial systems, and military systems.

Q: How does the cost of implementing N+1 or 2N redundancy compare to the cost of other types of redundancy?

A: The cost of implementing N+1 or 2N redundancy can vary depending on a number of factors, including the complexity of the system, the number of components involved, and the cost of the components themselves. In general, however, N+1 and 2N redundancy tend to be more expensive to implement and maintain than some other types of redundancy, such as hot standby or failover.

One reason for this is that N+1 and 2N redundancy require more components than other types of redundancy, which can increase the upfront cost of the system. For example, an N+1 redundant system will require one more component than is strictly necessary to perform the required function, while a 2N redundant system will require twice as many components. These extra components add to the overall cost of the system.

In addition, maintaining and troubleshooting an N+1 or 2N redundant system can be more complex and time-consuming than other types of redundancy, which can also increase the overall cost.

On the other hand, the increased reliability and availability provided by N+1 and 2N redundancy can justify the additional cost in some cases, particularly in mission-critical systems where downtime or failure is not acceptable. In these cases, the cost of implementing N+1 or 2N redundancy may be outweighed by the benefits it provides in terms of increased reliability and availability.

Q: What are the potential drawbacks of using N+1 or 2N redundancy?

A: Several potential drawbacks to using N+1 or 2N redundancy:

  1. Cost: As mentioned earlier, one potential drawback of N+1 and 2N redundancy is that they can be more expensive to implement and maintain than other types of redundancy, due to the need for extra components and the increased complexity of the system.
  2. Complexity: N+1 and 2N redundancy can also be more complex to implement and maintain than other types of redundancy, as they require more components and a more sophisticated system architecture. This can make it more difficult to troubleshoot and maintain the system.
  3. Increased risk of failure: While N+1 and 2N redundancy can increase the reliability and availability of a system, they can also introduce additional points of failure. For example, if the component that is used to switch between the active and standby components fails, the system may not be able to fail over to the standby component as intended.
  4. Decreased performance: In some cases, using N+1 or 2N redundancy can lead to a decrease in performance, as the extra components can introduce additional overhead and reduce the overall efficiency of the system.
  5. Compatibility issues: N+1 and 2N redundancy may also require the use of components that are compatible with one another, which can limit the choices available and increase the cost of the system.

Overall, while N+1 and 2N redundancy can provide many benefits, they also come with a number of potential drawbacks, including increased cost, complexity, and risk of failure. It is important to carefully consider these trade-offs when deciding whether to use N+1 or 2N redundancy in a given system.