Project Management

6 9s Availability and Why Should You Care?

Harry 3 min read
6 9s Availability and Why Should You Care?
Photo by Taylor Vick / Unsplash
Table of Contents

Many online services you use come with SLAs and promised uptimes. You may see these in the form of 99.9%, 99.99% and going up all the way up to 99.9999% (6 9s).

But what do they mean and how do they impact you and your business? Let's find out!

What is an SLA?

A SLA is an abbreviation for a Service Level Agreement. This is an agreement between you and the service you are transacting with which will provide you with the level of uptime you can expect from them.

So why is this important?

For a hosting company, for example, they may promise you 99.9% uptime within their SLA before any compensation is due to you.

But let's say you are reselling hosting for your clients. If your hosting provider only promises 99.9% uptime. There's no way you should promise anything higher to your client, as that puts your reputation at stake should you fall short of your hosting provider's SLA.

What is 6 9s Availability?

Now that we know what an SLA is, let's take a look at what 99.9999% (6 9s) promises.

  • 99.9% (3 9s) equates to a yearly downtime of no more than 8h 41m 38s.
  • 99.99% (4 9s) equals to 52m and 9.8s.
  • 99.999% (5 9s) equals to 5m 13s
  • 99.9999% (6 9s) is equal to no more than 31s downtime the entire year!

So you see, 6 9s is quite a promise to make. You don't want to promise an SLA you can't keep, but you also need to be sure you can financially sustain an endeavour.

Why Should You Care About 6 9s SLAs?

To begin this answer. Think how connected we are today and the services you financially depend on. If you're an e-commerce business and your payment provider or your website is down. You are losing sales. At the same time, your customers are frustrated and it will negatively hit your reputation.

In the more extreme cases, would you feel safe flying on an airline with a 99.9% SLA? I doubt it. This is where 6 9s are essential - in the places where you would find there is a threat to life or nationwide stability should there be an issue. Rather than an SLA being a target here, it is a minimum requirement for such services to operate.

This is why it's important to establish an SLA and set a goal for the highest uptime possible. It's also important to ensure any third-party vendors you depend on have adequate SLAs so you aren't left out in the cold.

But also consider the following questions:

  • How much do you stand to lose with a lower SLA?
  • How much will it impact you financially to target a higher SLA?

You need to find the point where you can balance the cost of what you'll lose vs. the cost of what you'll spend on hitting a higher target. Higher SLAs require more resources and failsafe solutions - which don't come cheap.

If High Availability (HA) is important to you and your business, then you will want to aim for the lowest downtime possible. Even if that comes at higher cost.


Make no mistake, we'd all love to live in a world of 100% uptime SLAs. But still, 6 9s can be a huge financial undertaking. This is why it's important to target what is reasonable for your business.

If you have a period of low traffic (ie, overnight). You can safely perform maintenance without the fear of huge financial consequences. Your infrastructure can be much simpler and less resilient compared to a service that is essential to human life, requiring several failsaves.

Whereas the services powering our hospitals, airlines, and banking systems are expected to provide a minimum SLA otherwise the consequences are huge either financially, at the cost of lives, or both.


Harrk Blog

Programming nonsense, tutorials, and random musings about games and technology.

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