RSM_AFQ

Description:

Whether available frame queue threshold values used for reclaiming storage frames are too low.

Reason for check:

To avoid situations where the system does not start to reclaim storage frames soon enough, you should evaluate the values for storage. If you are running in ESA mode, both the MCCAFCTH and the MCCAECTH values are used. If you are running in z/Architecture® mode, only the MCCAFCTH value is used. For migrations to a 64-bit environment, this check is critical because using the same value that was used in ESA mode could introduce problems. IBM® suggests that the IEAOPTxx parameters are set as follows:

MCCAFCTH specifies the low and the OK threshold values for central storage. The lowvalue indicates the number of frames on the available frame queue when stealing begins. The okvalue indicates the number of frames on the available frame queue when stealing ends. You can monitor actual conditions on the RMF™ Paging Activity Report (RMF Monitor 1) or a equivalent performance monitoring product and adjust accordingly.
MCCAECTH specifies the low and the OK threshold values for expanded storage. The lowvalue indicates the number of frames on the available frame queue when real storage manager (RSM) frame stealing begins. The okvalue indicates the number of frames on the available frame queue when stealing ends. You can monitor actual conditions on the RMF Paging Activity Report (RMF Monitor 1) or equivalent performance monitoring product and adjust accordingly.

In 31–bit mode, the defaults are sufficient. For these two parameters, the defaults are MCCAFCTH=(50,100), and MCCAECTH=(150,300). The OK point for available frames in a 31-bit mode implementation is 400 frames, 100 from central storage and 300 from expanded storage.

For 64–bit mode (after the installations of APARs OW55902 and OW55729), the default values for MCCAFCTH are (400,600). These are IBM's minimum suggested settings. Although IBM suggests using the defaults, higher values are acceptable.

z/OS® releases the check applies to:

z/OS V1R4 and later, in both ESA and z/Architecture modes.

User override of IBM values:

The following shows the default keywords for the check, which you can override on either a POLICY statement in the HZSPRMxx parmlib member or on a MODIFY command. This statement may be copied and modified to override the check defaults:

UPDATE,
    CHECK(IBMRSM,RSM_AFQ),
    INTERVAL(ONETIME),
    SEVERITY(HI),
    PARM('AFQLOW(400),AFQOK(600)'),
    DATE('date_of_the_change')

Parameters accepted:

The number of frames for the MCCAFCTH LOW threshold (keyword: AFQLOW)
The number of frames for the MCCAFCTH OK threshold (keyword: AFQOK)
The number of frames for the MCCAECTH LOW threshold (ESA only, keyword: EXPLOW)
The number of frames for the MCCAECTH OK threshold (ESA only, keyword: EXPOK)

Reference:

For more information on MCCAFCTH and MCCAECTH IEAOPTxx parameters, see z/OS MVS Initialization and Tuning Reference. For more information on using the Paging Activity report, see z/OS RMF Report Analysis and the whitepaper, WP100269 “z/OS Performance: Managing Processor Storage in a 64–bit environment”.

Messages:

This check issues the following exception messages:

IARH100E

See the IARH messages in z/OS MVS System Messages, Vol 6 (GOS-IEA).

SECLABEL recommended for multilevel security users:

SYSLOW - see z/OS Planning for Multilevel Security and the Common Criteria for information on using SECLABELs.