This documentation focuses on the notion of services. We view the SAP system as a set of software and hardware components that are hierarchically assembled into the fully functioning system. The inter-relationship between the components of the SAP system is very important for high availability. The individual components deliver services to one another. This means that, if one component fails, the effect is felt by other parts of the system that rely on the delivery of services from the failed component to complete their tasks, especially if a single point of failure (SPOF) is involved. If you do not provide a backup in the event of failure, unplanned system downtime is the result.
How you protect SAP system services depends on your overall approach to high availability, for example, whether you are using a standard SAP system or a high availability SAP system. For more information on the difference, see System Classification (SAP NetWeaver AS). In a standard configuration, certain services are unprotected (for example, enqueue, message, and database) whereas in a high availability configuration you can protect vulnerable services.
In a high availability SAP system, you can replicate vulnerable services, such as the enqueue, message, and database services by using, for example, cluster solutions or switchover solutions. This protects such services against failure. For more information, see:
There are the following types of logical SAP service:
· Front-end or presentation
The following aspects are relevant to application services:
· High availability
This aspect looks at how you can maximize availability for the SAP system. For example, if there are at least two application hosts running dialog services and one of the application hosts fails, then the users are able to connect to the second application host running dialog services. Therefore, having dialog services on different application hosts improves availability.
The way you set up application services can also affect performance.
For more information, see Availability and Performance.
The SAP system offers great flexibility in its configuration. This section discusses the SAP system services and the architecture of the SAP system from the high-availability viewpoint.
A simple example of the idea of services is the central role played by hardware services in the SAP system. If a disk drive containing data vital to system functioning fails, other aspects of the system are also threatened. In service terms, the hardware has failed to deliver the required service, which has effects on higher-level services (for example, SAP services), possibly leading to system downtime.