In a mixed sysplex environment made up of systems at MVS™ SP Version 5 and OS/390® Release 1, each of those systems must have APAR OW19718 installed in order to coexist with one or more OS/390 Release 2 systems. The APAR allows the systems to use the SFM weights in a consistent manner. With this support, the system selects a coupling facility for structure allocation based on the level of the system invoking the IXLCONN service:

• A request from an OS/390 Release 2 and higher system uses the SFM weights as part of the coupling facility ordering process when selecting a coupling facility. If an SFM policy is not in effect in the sysplex, all system are considered to have equal weight.
• A request from an MVS SP 5.1 through OS/390 Release 1 system uses the default selection algorithm for coupling facility selection and does not factor in the SFM weights.