XCF_CF_STR_POLICYSIZE

Description:

Check that structures in the CFRM active policy do not have too large a difference between the value specified for INITSIZE and the value specified for SIZE. All specifications of INITSIZE in the active or pending CFRM policy should indicate an initial structure size of at least half the maximum structure size (as determined by the SIZE specification). The policy should not specify an initial structure size less than the maximum structure size when altering of the structure size is not supported (as determined by this check).

This is a sysplex-wide check (GLOBAL) , which means that it runs on one system but reports on sysplex-wide values and practices. A global check shows up as disabled for all systems in the sysplex, except for the one where it is actually running.

Reason for check:

Specifying different INITSIZE and SIZE values provides flexibility to dynamically expand the size of a structure for workload changes, but too large a difference between INITSIZE and SIZE may waste coupling facility space or prevent structure allocation.

When allocating the structure initially, whether INITSIZE is specified or not, the system attempts to build all control structures that will be required to support the maximum size of the structure. These control structures are built in the control storage allocation of the structure. For structures whose users do not allow structure alter, the control storage allocated to accommodate larger sizes is wasted. An INITSIZE value substantially smaller than the SIZE value might cause the following:

It might be impossible to allocate a structure at a size of INITSIZE, because the amount of control storage required to support the SIZE value might actually be larger than INITSIZE.
If the allocation succeeds, it might result in a structure with a proportionally large amount of its storage allotted to structure controls, leaving too few structure objects to be exploited usefully by the associated application.

IBM suggests that the INITSIZE and SIZE specification for structures be determined by the CfSizer (Coupling Facility Structure Sizer) tool:

http://www.ibm.com/systems/support/z/cfsizer/

Any INITSIZE specification for a structure should be at least half of the SIZE specification. If structure alter is not allowed by users of a structure, INITSIZE should not be specified for that structure.

z/OS® releases the check applies to:

z/OS V1R12 and later.

Parameters accepted:

None.

User override of IBM values:

The following sample shows the defaults for customizable values for this check. Use this sample to make permanent check customizations in an HZSPRMxx parmlib member used at IBM Health Checker for z/OS startup. If you just want a one-time only update to the check defaults, omit the first line (ADDREPLACE POLICY) and use the UPDATE statement on a MODIFY hzsproc command. Note that using non-POLICY UPDATEs in HZSPRMxx can lead to unexpected results and is therefore not recommended. End of change

ADDREPLACE POLICY[(policyname)] [STATEMENT(name)]
UPDATE
CHECK(IBMXCF,XCF_CF_STR_POLICYSIZE)
SEVERITY(MED) INTERVAL(004:00) DATE (20090707)
REASON('Your reason for making the update.')
VERBOSE(NO)

Verbose support:

Yes. All structures in the CFRM active policy are included in an IXCH0923I report when the check is run in verbose mode. A check can be put into verbose mode using the following methods:

Specify the UPDATE,filters,VERBOSE=YES parameter either on the MODIFY command or in a POLICY statement in an HZSPRMxx parmlib member.
Overwrite the NO value with the YES value in the VERBOSE column of the SDSF CK command display.

Reference:

For more information, see z/OS MVS Setting Up a Sysplex.

Messages:

This check issues the following exception messages:

IXCH0255E

See the IXCH messages in z/OS MVS System Messages, Vol 10 (IXC-IZP).

SECLABEL recommended for MLS users:

SYSLOW