BPXMCDS couple data set versioning

z/OS® UNIX allows different levels or functional versions of OMVS couple data sets to be defined. The following couple data set format levels or functional versions can be created using the IXCL1DSU utility.

Base format level (Version 1). This is the initial or base z/OS UNIX couple data set format level and is created when the OMVS couple data set is formatted using a version of IXCL1DSU prior to z/OS V1R4.
z/OS V1R4 format level (Version 2). This format level is created when the OMVS couple data set is formatted using a version of IXCL1DSU at z/OS V1R4 or higher.

OMVS couple data sets formatted with the z/OS V1R4 version of IXCL1DSU are required in order to use the enhanced shared file system algorithms that are available in V1R4. Systems at different system levels can access the V1R4-formatted z/OS UNIX couple data set as described in the following scenario.

After IPL-ing the z/OS V1R4 system, initialization processing for the shared file system function in the sysplex will be delayed until an OMVS couple data set formatted at the z/OS V1R4 level is made available as the primary couple data set.

Using the z/OS V1R4 version of IXCL1DSU, define new primary and alternate OMVS couple data sets.
Enable the new Version 2 couple data set as the primary couple data set as follows:
- If there is currently no primary OMVS couple data set enabled in the sysplex, use the SETXCF COUPLE system command to identify one. For example,
```
SETXCF COUPLE,TYPE=BPXMCDS,PCOUPLE=(POSIX.OMVS.CDS01,OMVSDS)
```
- Alternately, if there is already a primary OMVS couple data set enabled in the sysplex (by another active system in the sysplex), use the SETXCF COUPLE system command to enable the version 2 couple data set as the alternate couple data set and then use the SETXCF PSWITCH system command to switch the alternate couple data set to the primary couple data set.
```
SETXCF COUPLE,TYPE=BPXMCDS,PSWITCH
```

These commands should be issued from a system where the OMVS couple data set is enabled as the primary. Enabling a version 2 OMVS couple data set as the primary couple data set is transparent to other active systems in the sysplex that are configured for shared file systems in a sysplex.

Once the version 2 OMVS couple data set is enabled as the primary couple data set in the sysplex, shared file system initialization processing on the z/OS V1R4 system should resume.