High availability refers to how long a component, website, network, or system can be continuously running or stay operational. A system, website, network, or component with a high availability could be described as 100% operational. While this is usually never the case, companies generally use the ‘five 9’s” system to rate their product’s or system’s availability. Five 9’s refers to a 99.999% of availability. Having a component or system that has a 99.999% availability would equal to about 5.39 minutes of downtime, whether planned or unplanned, in a year. Having this amount of downtime would generally be acceptable, especially if it was planned downtime. This occurs when there needs to be maintenance or updating on the component or system; however, many try to achieve the 24X7 model of availability.
Websites, for example, should be available 24 hours a day, 7 days a week. Even having a few minutes of downtime for a busy website can result in lost revenue or a reduction of confidence in the site. In the perfect world, the website, network, system, or component should be up available 24X7. This goal is costly and hard to reach. However, there are some ways to help one achieve it. Backing up components are always a great way to increase redundancy. For example, using the proper level of RAID can ensure that your fault tolerance is high; if one disk fails, another can take over. Using different types of data storage is also recommended, such as implementing Cloud storage. One can also use a UPS (uninterruptable power supply) to ensure power is maintained through the event of a failure. Trying to achieve high availability can strike terror into the hearts of many companies, especially start-ups, as their popularity and momentum can be quickly reduced if their website, for example, is even down for a few minutes.
Rouse, Margaret. (2010). 99.999 (Five nines or Five 9s). Retrieved from .