The Record Access Bias keyword for data class definitions in ISMF is expanded to include all the possible values which could previously be specified using the JCL AMP parameter’s ACCBIAS keyword. In addition, the JCL AMP parameter’s ACB RMODE31 keyword can now be specified in ISMF data class definitions. You can set these attribute values with the Data Class Define or Alter panels in ISMF.
The expanded list of options in the Record Access Bias keyword in the ISMF Data Class panels includes all the mutually exclusive SMB options (SYSTEM, USER, SO, SW, DO, DW, with a default of USER). Using a data class definition, you can modify these record access bias values without having to edit individual JCL statements, and the modification is no longer limited to one single job step.
The new ACB RMODE31 keyword lets you specify all the same values as the JCL AMP parameter supports: ALL, BUFF, CB, or NONE, with NONE as the default.
The JCL AMP specifications continue to take precedence over the specifications in the data class, and the data class specifications take precedence over the ACB specifications.
For more information about these new data class attributes and about VSAM system-managed buffering in general, see the topic Tuning for System-Managed Buffering in z/OS DFSMS Using Data Sets.