CICS®
system programmers must consult with their MVS™ system programmers to plan for the storage that is required by the log
streams required 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:
Primary storage, which holds the most recent records that were
written to the log stream. Primary storage can consist of either of
these areas:
A structure in a coupling facility. Log data written to the coupling
facility is also copied to either a data space or a staging data set.
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.
Auxiliary storage. When the primary storage for a log stream becomes
full, the older records automatically spill into auxiliary 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.
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 1 and Figure 2. Figure 1. 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 in the
coupling facility and either space in a staging data set or a data
space in the same MVS image as the system logger. Auxiliary 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 auxiliary
storage data sets.
Figure 2. 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. Auxiliary storage
consists of a series of data sets on disk storage, which hold successive
copies of the single staging data set. Tertiary storage is the DFHSM
storage holding older levels of the auxiliary storage data sets.
