Continuous availability ensures that data or services can always be accessed, even in the event of errors or malfunctions. Redundancy is key, with backup systems and software managing transitions. It is measured as a percentage of time available, with 99.99% being the goal for critical systems.
Continuous availability is a standard, or goal, for many information technology (IT) professionals, especially server administrators, when it comes to accessing data. This standard means that data on a server or other service can always be accessed, even if there is some kind of error or malfunction with software or hardware. This availability can be implemented in a variety of ways, often involving redundancy in hardware and software, backup systems in case of failure, and software that manages transitions between systems invisibly. Continuous availability has become increasingly important as businesses both vital and non-vital have become more dependent on digital information and technology.
The primary goal for continuous availability is that data or a service is always available to customers and employees. An online retail business, for example, wants this availability to ensure that customers can access the company’s website and complete purchases at all times. Air traffic controllers need the continuous availability of flight tracking systems to ensure that airplanes are able to navigate the skies safely, land and take off without problems. There are several ways that network administrators and other IT professionals strive for this type of availability.
Redundancy is, perhaps, the key concept in creating a system with continuous availability. This means that for every software and hardware component of a system, there is at least one backup that can be used in case of failure of the main component. If the fans of a bank of servers fail, for example, it can lead to the entire server overheating and crashing, resulting in a loss of availability for clients attached to that server. By having backup fans for a server, however, continuous availability can be better maintained. Other measures can then be used to notify technical support that the fans have stopped working, so they can be fixed while the backup fans are being used.
Continuous availability is often measured as the percentage of time a server or system is available. This is usually in terms of a year, where 99% availability would mean the system is down 87.6 hours per year, whereas a system with 99.99% availability is only down about one hour per year. While just one hour of downtime per year may seem like very high availability, one hour of downtime for an air traffic control system could be catastrophic. Downtime is caused by planned or unplanned outages, which refer to times when a system may be down for scheduled maintenance or is down due to a failure within the system.
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