When an application or computer system is supposed to be running and isn’t, it impacts productivity and costs money. When an application becomes unavailable, the work that it was doing simply stops. At best, such an outage simply results in lost productivity.... High Availability attempts to specify an amount of time as a percentage of the intended duty cycle that a system must be functional.
High Availability Technical Primer
The use of computers in our daily business and personal lives is pervasive. We literally cannot drive a car, travel, shop at any store, or perform our jobs without the use of computers. In many cases, there are no manual procedures available to replace what computers do for us. Email, Internet Web, and instant messaging have replaced U.S. Postal Mail as our preferred method to communicate.
When these systems and the applications are not available, due to technical problems, we suffer loss of productivity at work and inconvenience in our personal lives. It is not difficult to calculate the real costs incurred when critical business systems are down. More serious consequences occur when critical systems such as traffic control, medical life support, or health services systems are not functioning.
Whatever the situation, when an application or computer system is supposed to be running and isn't, it impacts productivity and it costs money. When an application becomes unavailable, the work that it was doing simply stops. At best, such an outage simply results in lost productivity--the application will be up and running some time later, and the work will be completed later. More serious consequences can occur through safety, legal actions, fines or simply negative publicity.
The impact of downtime will vary from business to business and within a business from application to application. Global businesses or Internet-enabled businesses may need order-entry applications to be continuously available. Customer support staff may need access to data 24 hours a day with a response time that is measurable in seconds. On the other hand, some departments may need access during normal business hours only and can tolerate somewhat sluggish responses. The cost of the measures taken to ensure that systems keep running must be aligned with the risk (both human safety and financial) and the associated benefits.top