What is High Availability?

High Availability, or HA, refers to the objective and associated strategies to maintain system uptime and accessibility against threats of unexpected performance and system failure. For many businesses it is essential to operate highly available systems. As one of the leading and longest established companies offering highly available software solutions, discover in depth how High-Availability.com's RSF-1 Highly Available solutions and services can help your business operations.

An Enterprise IT system may consist of any number of key dependencies including hardware components, utilities, software and access points, all of which must be maintained to ensure system integrity and user availability. The failure of any single dependency may threaten the service viability of the entire system resulting in system downtime.

Illustration showing high availability word cloud

What is system uptime or downtime?

Downtime describes the actual time a system is unavailable and includes the time to recover from unexpected failures as well as planned maintenance time windows.

Conversely, system uptime represents the time a system has been fully operational as a percentage of total potential time availability and is often described by a number of nines. Three nines for example refers to 99.9%, which when taken over a calendar year, represents approximately one business day or 8.5 hours. Four nines (99.99%) over a year represents just under an hour, and five nines (99.999%) only five minutes. To achieve five nine service availability therefore requires building, designing, maintaining, and running a system that will remain completely operational with planned maintenance windows for all but just five minutes across a calendar year.

What uptime can be achieved without High Availability software?

Expecting to achieve 100% uptime capability without deploying a comprehensive high availability strategy is an extremely unrealistic prospect relying solely on luck and is a highly unlikely target to achieve. All system components will fail at some point, utility provision is not guaranteed, human errors will occur and unpredictable environmental risks will arise. By architecting optimal system design practice, using high quality enterprise-grade components with low failure rates and using robust and comprehensive operational procedures, it is possible to significantly reduce the likelihood of failure, but this approach alone is not enough.

What are the main benefits of a highly available system?

  • Protection of business revenues and data assets
  • Enhanced service uptime
  • Automatic and predictable recovery from failure
  • Non-disruptive system upgrade capability
  • Failover testing - implement regular "fire drill" tests to ensure key systems and service failover is robust and reliable

Find out how to set up the HA configuration and FAQ's on high availability clusters.

Implications of High Availability?

As there is almost always a financial element associated with system downtime, whether through loss of direct revenue, productivity, reputation, or consequential loss, ensuring key systems operate with a high level of availability and accessibility is critical.

As most IT service contracts are governed by Service Level Agreements (SLAs) including provisions for server uptime, service availability guarantees and penalties, it is important to design, build and run systems that operate within the prescribed service availability requirements. Enhancing system High Availability is therefore not just aspirational but absolutely essential.