Degrees of availability
The terms high availability, continuous operation, and continuous availability are used to express how available a system is.
High availability
High availability refers to the ability to avoid unplanned outages by eliminating single points of failure. The absence of unplanned outages is a measure of the reliability of the hardware, operating system, and database manager software. Another measure of high availability is the ability to minimize the effect of an unplanned outage by hiding the outage from the users. This hiding can be accomplished by quickly restarting failed components with the help of an automation program such as IBM Z® System Automation.
Continuous operation
Continuous operation refers to the ability to avoid planned outages. For continuous operation, there must be ways to perform administrative work and hardware and software maintenance, while the application remains available to the users. This continuous operation is accomplished by providing multiple servers and switching users to an available server at times when one server is made unavailable. Using Db2® data sharing with Db2 connection failover is an example of how continuity is accomplished in an SAP environment. Topics SAP availability benefits provided by IBM Z through Disaster recovery describe how a number of planned outages can be avoided by taking advantage of Db2 data sharing and Db2 connection failover.
Continuous availability
Continuous availability combines the characteristics of high availability and continuous operation to provide the ability to keep the SAP system running as close to 24 hours a day during 365 days a year as possible.