Coupling facility or DASD-only?

The CICS® log manager supports the DASD-only option of the MVS™ system logger. 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 you define to use the coupling facility and which to use DASD-only:
  • A coupling facility log stream must be used if you want to allow simultaneous access from CICS regions running in different MVS images. (Simultaneous access to a DASD-only log stream is limited to CICS regions in the same MVS image.)

    For example, assume that you are using RLS and have several CICS application-owning regions (AORs) running on different MVS images. Because the forward recovery log must be accessible from all the AORs, it must be defined as a coupling facility log stream. A CICS system log, on the other hand, is accessed only by a single CICS region, and can therefore always be defined as a DASD-only log stream.

    Without a coupling facility, you cannot share general log streams across MVS images.

  • For optimum availability, avoid defining all your CICS log streamsto use structures in a single coupling facility. See Coupling facility log streams for more information.
  • DASD-only log streams are easier to define and administer than coupling facility log streams.
  • The CPU cost of a log write to a DASD-only log stream is greater than that of a write to a coupling facility log stream.
  • If the amount of available coupling facility space is limited, you might want to define some DASD-only log streams to minimize the amount of space allocated to log structures.

Note that you can define a single-system sysplex, which must use a sysplex couple data set, with PLEXCFG=MONOPLEX. This definition is required for stand-alone MVS systems that use MVS system logger facilities. Also, define sysplexes that have two or more MVS images with PLEXCFG=MULTISYSTEM.