Uptime.com Blog

Uptime vs. Availability: What’s the Difference and Why It Matters

In June 2019, a curious thing happened. Students were forced to go fully analog, putting pencil to paper when they couldn’t log in to their Google Classroom accounts. Avid media consumers sat staring blankly at buffering YouTube videos. Gmail notifications came to a screeching halt as inboxes sat eerily quiet.

It wasn’t that the Google Cloud Platform had crashed — far from it. For most of the world, the systems were technically still “up.”

However, for those trying to access instances in six regional data centers in North and South America, that technicality didn’t matter. The service might have been online, but the sudden spike in latency, errors, and connectivity loss rendered it functionally unavailable.

The takeaway of this “cataclysmic” event revealed an important truth: Uptime might show that your systems are operational, but availability tells the real story.

Let’s examine the differences in uptime vs. availability and why you should monitor both to get an accurate picture of your service reliability.

What Is Uptime?

Of the two measurements, defining uptime is a more straightforward quantification of reliability, expressed as a percentage of time that a digital system or service was operational in a particular period.

Learning how to calculate uptime just requires finding the ratio of uptime to downtime within a month or year, like so:

Uptime Metrics

Availability and uptime metrics and percentages are often described in terms of “nines.” Here’s a quick reference chart for the first three levels of performance:

Why Does Uptime Matter?

Because it’s easy to understand and measure, uptime is a service level objective (SLO) that communicates system reliability to customers. A high uptime percentage tells them they can count on your service being available when needed. Sysadmins also use internal uptime monitoring as a first line of defense in predicting downtime events.

However, relying solely on uptime can give a false sense of security if you don’t assess system performance in broader terms. Even if you could tout being operational 100% of the year, users can still experience performance issues like slow response times or connectivity problems. That’s where availability comes into play.

What Is Availability?

Comparing uptime vs. availability, unlike the binary “up or down” measure of uptime, availability reflects the entire experience, accounting for performance issues like slow response times or system errors even if the service is technically still online.

The formula for calculating availability is similar to uptime but includes periods when performance issues make the system difficult or impossible to use. Let’s use our example from the uptime section: A business reported 117 minutes of unscheduled downtime and 99.9% uptime. However, we also need to factor in instances where users experienced degraded performance, reducing the system’s availability.

In addition to downtime, the system faced these issues:

• An hour of scheduled maintenance per month netted 720 offline minutes
• Increased error rates due to system overloads, causing another 459 minutes of disruption
• High response times during peak hours led to 800 minutes of poor performance

While neither of these problems took the system completely offline, we do need to account for those additional 2,096 minutes in our availability calculation:

Based on the availability metrics, the site was unusable for one day, 10 hours, and 56 minutes rather than 8 hours and 45 minutes.

Why Does Availability Matter?

As our calculations demonstrate, uptime tells you how often your system is operational but doesn’t consider the user experience.

Even with 99.9% uptime, poor availability due to degraded performance is not what customers want from their digital interactions. Thus, the only way to truly monitor your site’s usability is by combining the uptime metrics for at-a-glance statistics and availability metrics to keep your digital product performing well under all conditions.

Availability vs. Uptime Differences Summarized

Don’t Be Fooled by the Watermelon Effect

There’s no better way to visualize the relationship between uptime and availability than the watermelon effect. This term refers to a situation when your uptime metrics look “green” from the outside, but the availability metrics are in the “red” underneath the surface.

Take the example of a SaaS company providing an invoicing platform for small businesses. Their uptime is in the “green,” reported at 99.9%. But beneath that, the system freezes or times out whenever the user attempts to generate a client-facing invoice.

Internally, the SaaS provider sees 99.9% uptime and assumes everything is operating smoothly. Meanwhile, it’s practically unusable for anyone who requires the customer invoicing feature.

This mismatch between uptime and real-world usability is why businesses should keep abreast of all the metrics available, a feat made easier with Uptime.com’s comprehensive performance monitoring tool.

Within one intuitive dashboard, you can curate a selection of metrics — response times, error rates, uptime, availability, and more. Get started with a 14-day free trial today to see how Uptime.com can keep your digital services running smoothly.

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