Defining coupling facility structure names for sysplex data sharing

These names are passed to IMS in the CFNAMES control statement in the DFSVSMxx member. The purpose of this statement is to let you select which of the structures, previously defined in the z/OS® policy, is to be used at run time.

You can specify one or more CFNAMES control statements. Each statement can contain one or more keyword parameters. Each keyword parameter must be specified in its entirety on a single CFNAMES statement. A specific keyword parameter can not be continued from one CFNAMES statement to another. If keyword parameters are duplicated, the first parameter encountered is used and the others are registered with an error message.

The structure names that you specify in the CFNAMES control statement can be 1 to 16 characters long. All keywords in the statement must be coded, but null values for the CFOSAM and CFVSAM keywords are allowed.

IRLM

If you do not specify structure names in this PROCLIB member or specify only the IRLM structure name, the default is for the environment defaults to use two-way data sharing using the notify protocol.

If the IRLM and OSAM or VSAM structure names do not match the structure names known to the coupling facility at the time of the IDENTIFY, the IDENTIFY is rejected and IMS initialization fails. The first IMS in a data sharing group that identifies itself to the IRLM, sets the data sharing environment for all other IMS subsystems connecting to the same IRLM structure. The first IMS, in other words, sets the structure names for the coupling facility. If, for example, the first IMS does not specify structure names in this PROCLIB member, no other IMS subsystems identifying to this IRLM can specify structure names (except for an IRLM structure name matching the one set by the IRLM); otherwise, the IDENTIFY is rejected and IMS initialization fails. The same thing happens if the first IMS specifies all three structure names and, later, another IMS subsystem tries to identify using one or more different structure names.

OSAM

If you are using OSAM sequential buffering, the OSAM structure registers SB buffers in the coupling facility's cross-system buffer invalidation process.

Control statements for defining coupling facility structure names for sysplex data sharing

CFNAMES must appear in column 1. No blanks can appear between the keywords.

Syntax for defining coupling facility structure names for sysplex data sharing

Parameter descriptions for defining coupling facility structure names for sysplex data sharing

CFNAMES

Specifies the coupling facility structure names that must be passed to IMS.

CFIRLM=aaaaaaaaaaaaaaaa

Specifies the coupling facility lock table structure name for the IRLM.

CFVSAM=bbbbbbbbbbbbbbbb

Specifies the coupling facility XI structure name for VSAM.

CFOSAM=

You can specify either the coupling facility name only, or the coupling facility name and directory-to-element ratios.

cccccccccccccccc

Specifies the coupling facility structure name for OSAM.

(cccccccccccccccc,DIRRATIO,ELEMRATIO)

Specifies the coupling facility structure name for OSAM and the directory-to-element ratio that the CF uses to configure the structure for data caching.

The DIRRATIO and ELEMRATIO subparameters are optional. The installation uses the CFRM policy to specify the size of a cached structure. When the structure is allocated, its storage is subdivided to reserve space for directory entries and data elements. The directory-to-element ratio determines the proportion of the cache used for directories and data elements. The ratio is expressed as a pair of whole numbers and is used when a connection is made to the structure. The directory-to-element ratio should reflect the average number of data elements per cache entry. The size of each data element is 2 KB. OSAM data is contained in the coupling facility as multiples of 2 KB data elements. If the ratio is incorrect for an installation's use of the structure, frequent rejections of cache requests can occur because either the cache or the cache structure is full.

The result of dividing the ELEMRATIO value by the DIRRATIO value must not exceed 16, the maximum number of elements supported by an OSAM structure. If the result is greater than 16, the specified ratio is rejected and IMS supplies a ratio.

The DIRRATIO value represents the directory part of the ratio and ELEMRATIO represents the element part of the ratio. Both subparameters are coded as one to three digits. If you choose to specify one of the subparameters, you must specify both.

If you omit the DIRRATIO or specify a value of zero, IMS provides a default DIRRATIO of 1:0. If DIRRATIO specifies a non-zero value and ELEMRATIO specifies zero, IMS supplies a ratio of 1:0. This ratio causes the coupling facility to configure the OSAM structure to preclude data caching. If data caching is precluded, the OSAM structure only supports buffer invalidation processing and does not support cache data.

If you omit the DIRRATIO and ELEMRATIO subparameters, or if they fail validation of the maximum elements number, IMS provides a default ratio.

IMS supplies a default ratio of 999:1. This ratio causes the coupling facility to configure the data caching OSAM structure to optimize buffer invalidation and not data caching. While data caching might be possible, the structure provides limited space for data elements.

Related reading: For additional information about sysplex data sharing, see IMS Version 15.4 System Administration.

Specifies the coupling facility XI structure name for OSAM.