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The Five 9s: Reliability & Availability

by Margaret Joy

The five 9s rank system uptime based on minutes of downtime that occur per year. High availability is key for reliable service: the more 9s the better.

The term five 9s refers to system and network availability. It’s a metric that measures uptime—that is, how often your system is up and running. Typically it’s measured in percentage of availability per year, usually ranging from 99% to 99.999% of the time. That may seem like a pretty easy target to hit, but it’s actually tougher than you think to rack up those thousandths of percentage points. 

Breaking Down Downtime

Some graphs break down downtime incrementally starting from one 9 (90% uptime), but colloquially the 9s metric typically covers 99% to 99.999%, with an additional 9 at each level. Here’s a simple table to explain downtime:

A simple table showing downtime per year for 1 through 5 9s
One 9 to five 9s availability (Dell).

You can see how each additional 9 is a fairly big jump. Common knowledge tells us that any advertisement about 100% uptime is an instant red flag. Everything has downtime throughout the year—that’s a fact. Downtime is normal! It’s how systems update, and theoretically that should take minimal time. Longer downtime comes from cyberattacks and other disastrous disruptions. If you suffer a heavy storm or deal with a nasty DDoS attack, for example, you would see your availability metric drop—and fast. 

For a more detailed analysis, check out AWS’s five 9s breakdown:

A detailed breakdown of five 9s availability rankings

Let’s give this a practical example. Anything lower than five 9s availability is considered unacceptable for emergency services. Can you imagine calling 911 and their system is down? That's not okay. If you need emergency medical services, time is of the essence. They can’t afford anything below high availability. (Even six 9s recently entered the lexicon, clocking in at just 31.6 seconds of downtime in a year.) 

To shift perspective to your average business, let’s discuss how five 9s availability ties into business reliability.

Five 9s Reliability and OnSIP Business VoIP

On the surface, five 9s availability may seem like more of a selling point, the kind of thing you highlight to sway potential customers. But it’s much more than a line item in a pros and cons list. High availability is closely tied to business continuity. As a UCaaS company, much of our blog content is dedicated to that topic. Cybersecurity and disaster recovery, cloud resilience and reliability—there are loads of factors that play into business continuity. System uptime is yet another item in that whole sphere. You need high availability to be reliable and strong cybersecurity practices to protect your availability. A single hour of downtime not only decimates your high availability status but can cost a business well over $100K per hour

The reliability cycle centers around strong system architecture, like what we’re seeing in hyperscale data centers or privacy by design. When it comes to choosing a business VoIP service, it’s imperative that you look for one with known and consistent reliability. 

Graphic showing a customer review of OnSIP highlighting our service and reliability

Communication to customers is key at all times, of course, but particularly during any service disruptions. It’s a point of pride for us here at OnSIP that we provide one of if not the most reliable cloud VoIP system. We made sure of that from our very start back in the mid-2000s. By building our entire platform from scratch, we were able to incorporate guaranteed redundancy. Our patented system is geographically distributed, which means that our hardware is spread out across the US. We’re able to balance demand loads regardless of natural disasters or how fast our customers’ needs scale. 

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