Understanding couple data set coexistence

The IXCL1DSU format utility allows you to specify different maximum values for some couple data set parameters. These values are based on the version of the code installed on your system. For example, the initial maximum value for the CFRM parameters STR and CONNECT was 64. Subsequent updated versions of the utility allowed you to specify 255 as the maximum value for CONNECT and 1024 as the maximum value for STR. These increases cause a corresponding increase in the physical size of the CFRM couple data set and the individual records the data set contains.

In a sysplex where not all systems support the same couple data set types, or maximum values for particular couple data set types, special attention must be given to uplevel and downlevel data sets. (In this context, an uplevel couple data set refers to one that has been formatted to:

Support a new item type that did not exist in a prior version of the couple data set.
Support more instances of a particular type of item than were supported in a prior version of the couple data set.
Support both examples cited above.

A downlevel couple data set is one that has not been formatted as described for an uplevel couple data set.

The following coexistence concerns should be noted for uplevel and downlevel couple data sets:

XCF does not allow you to install an uplevel couple data set on a system in a sysplex in which one or more systems do not include the code for a newer version of the format utility (and for the higher maximum values specified in the utility).
For example, you cannot issue a SETXCF COUPLE command to bring into use a CFRM couple data set formatted for 255 structures in a sysplex in which the code support for the 255 maximum has not been installed on all systems.
When defining your primary and alternate couple data sets, the system does not allow you to mix couple data sets formatted at different versions when running in a sysplex in which one or more systems do not include the code for a newer version of the format utility (and for the higher maximum values specified in the utility).
For example, do not specify a primary couple data set formatted for 64 structures and an alternate couple data set formatted for 255 structures on a system on which the code support for the 255 maximum has not been installed.