In the data center industry, we tend to use the terms ‘availability’ and ‘reliability’ somewhat synonymously, and while they are related, they are not the same thing. On one hand, reliability is defined as the probability of failure-free system operation over a specified time in a given environment for a given purpose. Availability on the other hand is defined as the probability that a system, at a point in time, will be operational to deliver the requested services. Availability is measured in terms of percentage of uptime vs. downtime, where the closer to 100%, the better. (This where the ‘9s’ come in to play – 99.9%, 99.99%, 99.999%, etc.).

It’s important not to confuse availability and reliability. Availability takes into account the time that the system is out of service, therefore, unreliable systems can technically have high availability if there is a short restart time. This is not useful in data centers as IT systems will typically take far longer to restart than M&E systems.

For more on data center risk management, check out our recent webinar titled, Data Center Risk Management: The Importance of Mitigating Risk to Maximize Resiliency.