Datacenter Redundancy N+1, N+2 vs. 2N vs. 2N+1

While it might be one of the most annoying things on earth when it comes to a parent being asked “are we there yet” a dozen times within a 30-minute ride, redundancy is everything for data centers. Redundancy systems can prevent outages from having a negative impact on a data center’s reputation, reliability, business operations, and ultimately their financial bottom line. What does redundancy entail? Why’s it important? What are the redundancy system options for a data center? Let’s explore.

What Is Data Center Redundancy And Why’s It Necessary?

So, what is redundancy in technical engineering terms? It’s basically a failsafe or backup in the form of a system’s critical components/functions being duplicated in ways that bolster the system’s reliability. In other words, the system is more likely not to fail when the primary source of power goes out.

Now, how does redundancy apply to data centers? The focus here is on the amount of spare power needed to provide customers a backup power supply when power outages occur, which is a huge causative factor in datacenter downtime. No data center likes to hear the word “downtime,” but it’s a reality that happens to data centers across the U.S. every year.

A 2013 study on data center outages by the Ponemon Institute surveyed 584 entities with some operational responsibilities for data centers. The findings showed the following statistics:

• 85 percent experienced loss of primary utility power within the last two years.

• Unplanned outages were experienced by 91% of the above respondents.

• The average data center shutdown time averaged two hours.

• Of those two-hour shutdowns, the downtime averaged over 90 minutes during each failure.

Why do outages happen? Most will immediately say weather, right? But, weather isn’t the only source of outages. From internal or external equipment failure to someone hitting a power line with heavy outdoor equipment, the possibility for an unplanned outage means that failure can happen to any data center and at any time.

Outages can cost data centers significant revenue losses, particularly if they’re driven by internet sales that require continual connectivity. Per hour of downtime each year, the average data center loses $138,000 in revenue. For big business like Amazon, those lost revenue numbers soar to over $1,000 per downtime second.

Redundancy Matters For Data Centers

The Ponemon study goes a long way in speaking to the importance of data centers everywhere implementing DCIM (Data Center Infrastructure Management.) If revenue matters, then downtime matters. If downtime matters, then prevention matters. If prevention matters, then redundancy is a must.

Larger entities generally have their servers at Tier 3 or Tier 4 data centers who counter unforeseen power outages with “sufficient” redundancy power systems. That said, not all these redundancy systems are equal in terms of value and protection. Look to how the system is set up to determine the degree of failsafe protection it offers, specifically whether the redundancy system is a N+1, 2N, or a 2N +1 setup.

N+1, 2N, and 2N+1 Redundancy Systems: What’s The Difference?

N+1 System

Imagine that you’re having a party with 20 invited guests. You’d naturally need 20 plates, right? That’s your “n” value. But, what if someone brings an unexpected guest or someone shows up out of the blue? The +1 accounts for extra plate you may need.

In data center language, it’s called a parallel redundancy – the number of UPS modules you need for essential connected systems.. plus one, and it offers a UPS (uninterruptible power supply) that is available 24/7. The result is a decreased chance of downtime.

N+1 systems do have redundant equipment, but the system is still operating on a common feed/circuit on at least one common point. This fact leaves the system open to failure. A fully redundant system has completely separated feeds as a failsafe. So, the degree of protection here is better than no failsafe, but things could be better.

2N System

Again, you’re having a party with the 20 guests. What a 2N does is double the expected number. So, you’d have 20 extra plates for your party, not just one.

For data centers, a 2N redundancy system means double the equipment that’s needed for essential operations. Each run separately with no possible common points of failure. It’s a fully redundant system capable of offering an independent failsafe should an extended power outage happen and you need to keep things running. Think of it like having a spare car ready to roll if your primary vehicle gets a flat tire.

2N+1 System

This redundancy system is a combination of the above two. It doubles the amount of equipment needed and also has an extra piece for good measure. It’s the most comprehensive redundancy system, but most data centers find the 2N to be adequate and more financially friendly.