Put simply, a highly available system is usable when the customer needs it. A system can be highly available while operating from 8 am to 5 pm, if that is all the business demands. The remaining time can be used for scheduled maintenance and repair.
Availability is defined as actual service divided by required service.
Overview The pervasiveness of computers in everyday life is increasing the demand for more highly available systems. Deregulation in the telecommunications industry, the Internet, and new entertainment services such as video on demand are creating opportunities for new computing platforms. The challenge in these industries is to provide reliable services at competitive costs. Fault Tolerance versus High Availability 2. Redundant Configurations 3.