WADS migration considerations

IMS 15 introduced new changes to the write-ahead data set (WADS).

The WADS must be defined as a VSAM linear data set with a control interval (CI) size of 4 KB (4096-bytes), secondary space allocation of 0, and with the SHAREOPTIONS(3 3) parameter. The access method services (AMS) utility IDCAMS can be used to define the data set.

If the WADS for different IMS systems on different logical partitions (LPARs) share the same data set name, you must specify SHAREOPTIONS(3 3) for the WADS, even though the physical data sets are not shared between the systems.

Recommendation: Use different data set name for the IMS 15.4 WADS than the name used for the WADS in current IMS version. This allows you to predefine the IMS 15.4 WADS before shutting down the current IMS system. Otherwise, the WADS must be deleted and redefined after the current IMS system goes down and before the system is started as an IMS 15.4 system.

You can use the ZHYPERWRITE= parameter in the LOGGER section of the DFSDFxxx PROCLIB member to enable or disable the use of zHyperWrite to write to the WADS.

Example

The following JCL is an example of allocating the WADS:


//AMS EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *

DEFINE CLUSTER -
     (NAME(IMSA.WADS.VSAM) -
     VOLUME(VOL001) -
     CONTROLINTERVALSIZE(4096) -
     SHAREOPTIONS(3 3) -
     CYLINDERS (20 0) -
     LINEAR)
/*