The system logger configuration you use depends on whether or not you use a coupling facility.

Coupling Facility Log Stream Configuration: Figure 1 shows all the parts involved when a system logger application writes to a coupling facility log stream. In this example, a system logger application runs on two systems in a sysplex. Both instances of the application write data to the same log stream, TRANSLOG. Each system contains a system logger address space. A system logger application uses system logger services to access the system logger capabilities.

When a system logger application writes data to a coupling facility log stream, system logger writes the data to a coupling facility list structure associated with the log stream. Then, when the coupling facility structure fills with data, system logger off-loads the data to DASD log data sets.

You can optionally elect to have coupling facility data duplexed to DASD staging data sets for a coupling facility log stream.

Figure 1. A Complete Coupling Facility Log Stream Configuration

DASD-Only Log Stream Configuration: Figure 2 shows all the parts involved when a system logger application writes to a DASD-only log stream. System logger writes the data to the local storage buffers on the system, duplexing it at the same time to the DASD staging data sets associated with the log stream. Then, when the staging data set fills with data, system logger off-loads the data to DASD log data sets. Note that where duplexing to DASD staging data sets is an option for a coupling facility log stream, it is a required automatic part of a DASD-only log stream.

Figure 2. A DASD-Only Configuration