Setting up the environment for CICS log manager

CICS® system programmers need to consult with their MVS™ system programmers to plan for the storage that is required by the log streams needed by the many CICS log managers operating in the sysplex.

Each log stream is a sequence of blocks of data, which the MVS system logger internally partitions over three different types of storage:

  1. Primary storage, which holds the most recent records that were written to the log stream. Primary storage can consist of either:
    1. A structure within a coupling facility. Log data written to the coupling facility is also copied to either a data space or a staging data set.
    2. A data space in the same MVS image as the system logger. Log data written to the data space is also copied to a staging data set.
  2. Secondary storage--when the primary storage for a log stream becomes full, the older records automatically spill into secondary storage, which consists of data sets managed by the storage management subsystem (SMS). Each log stream, identified by its log stream name (LSN), is written to its own log data sets.
  3. Tertiary storage--a form of archive storage that is used as specified in your hierarchical storage manager (HSM) policy. Optionally, older records can be migrated to tertiary storage, which can be either DASD data sets or tape volumes.

See the different levels of log stream storage in Figure 10 and Figure 11.

Figure 10. The types of storage used by the MVS system logger. This diagram shows a log stream that uses a coupling facility. Primary storage consists of space in a structure within the coupling facility, and either space in a staging data set or a data space in the same MVS image as the system logger. Secondary storage consists of a series of data sets on disk storage to which the elements of the log structure in the coupling facility are mapped. Tertiary storage is the DFHSM storage holding older levels of the secondary storage data sets.
 This figure is described in the text.
Figure 11. The types of storage used by the MVS system logger. This diagram shows a log stream that uses DASD-only logging. Primary storage consists of a data space in the same MVS image as the system logger, and a single staging data set. Secondary storage consists of a series of data sets on disk storage to which hold successive copies of the single staging dat set. Tertiary storage is the DFHSM storage holding older levels of the secondary storage data sets.
 This figure is described in the text.

Coupling facility or DASD-only?

The CICS log manager supports the DASD-only option of the MVS system logger. This means that individual CICS log streams can use either coupling facility log structures or DASD-only logging.

Take the following points into account when deciding which log streams should be defined to use the coupling facility and which to use DASD-only:

Notes:
  1. Define a single-system sysplex (which must use a sysplex couple data set) with PLEXCFG=MONOPLEX. This is required for stand-alone MVS systems that use MVS system logger facilities.
  2. Define sysplexes that have two or more MVS images with PLEXCFG=MULTISYSTEM.
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