2. PERFORMANCE REPORTING ANALYSIS › 2.8 Sysplex Analysis › 2.8.4 Parallel Sysplex Concepts › 2.8.4.2 Controlling the Sysplex Environment › 2.8.4.2.2 Coupling Facility Resource Management

2.8.4.2.2 Coupling Facility Resource Management

The coupling facility is at the heart of a parallel sysplex
environment, and makes possible the sharing of data by
providing high-speed locking, caching and message/list
services between selected System/390 processors running
MVS/ESA SP 5.1 or above.

You manage a coupling facility through a policy.  Coupling
Facility Resource Management (CFRM) allows you to specify how
the coupling facility and attendant resources are to be used.
CFRM policy is created using an IBM utility which places
the information out on one or more couple data sets.  MVS and
multisystem applications use the definitions in the CFRM
policy when managing the coupling facility storage.

Storage in a coupling facility is divided into different
constructs call "structures."  These structures are used to
implement high-speed serialization and data sharing.  To
facilitate this process, the structures are divided into
three types: cache, list, and lock.  In addition to
structures, some storage in the coupling facility can be
allocated as a dedicated dump space for capturing diagnostic
information related to the structures.

Among other things, when defining a CFRM policy, you must
identify each coupling facility and structure, and define the
amount of space within the coupling facility that you want
for each structure.  More importantly, for performance and
capacity purposes, you can define preference and exclusion
lists for each structure in the CFRM.  These lists can be
defined as follows:

   o   A preference list is an ordered list of coupling
       facility names in which a particular structure can be
       allocated.

   o   An exclusion list is an unordered list of structure
       names with which the structure being defined should
       not share a coupling facility.

The system selects a coupling facility for structure
allocation based on the preference and exclusion lists in the
CFRM policy and the availability of storage in the coupling
facility.  However, the system will ignore an exclusion list
if it would prevent the structure from being allocated.

Keep in mind that for performance and recovery purposes, you
can distribute structures on different coupling facilities.
Having more than one coupling facility is almost essential in
a sysplex to avoid a single point of failure that would
prevent intersystem communication.