WADS support for zHyperWrite

In IMS 15, the IMS Logger uses the DFSMS Media Manager to write data to the write-ahead log data set (WADS). As a result, the WADS must be defined as a VSAM linear data set.

The DFSMS Media Manager enables the usage of the hardware features like High Performance FICON® for z Systems™ (zHPF), which increases I/O throughput, and zHyperWrite, which reduces latency time for synchronous replication products. For reading from the WADS, regular VSAM is used.

Start of changeTo enable or disable zHyperWrite for the WADS, you have the following options:
  • Use the WADS= keyword in the ZHYPERWRITE= parameter in the LOGGER section of the DFSDFxxx PROCLIB member. For more information, see LOGGER section of the DFSDFxxx member.
  • Start of changeWith APAR PH02149 (PTF UI61325) installed, you can use the WADS(Y) parameter in the UPDATE IMS SET(LCLPARM(ZHYPERWRITE()) command to dynamically enable zHyperWrite without a restart. For more information, see UPDATE IMS command.End of change
End of change

Migration considerations

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.

Recommendation: Use different data set name for the IMS 15 WADS than the name used for the WADS in current IMS version. This allows you to predefine the IMS 15 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 system.

Coexistence considerations

For XRF systems, both of the coexisting systems must be of the same IMS version.

Fallback

When you fall back from IMS 15 system to a previous version of IMS, ensure that you use a non-VSAM data set for WADS.

If you defined WADS data set names for IMS 15 during migration that were different from the names used by the previous IMS version, use the previous names for fallback. The fallback process replaces the reference to the WADS data sets systematically. Otherwise, the WADS must be deleted and redefined after the IMS 15 system is shut down, and before the system is started at the previous IMS version.

At the end of fallback, cold start IMS with the FORMAT ALL or FORMAT WA keyword.

Log record changes

The following log records are new or changed by this enhancement in IMS 15:

  • X'4507' - The following fields are added:

    • ST4507_WADSCIS, which specifies the number of control intervals in the WADS.
    • ST4507_FLG2 (X'40': ST4507_F2_ZHYPWADS)

  • X'4507' - The following fields are removed:

    • ST4507_WADSTRACKS, which specifies the number of physical tracks in the WADS data set.
    • ST4507_WADSBLKSTRK, which specifies the number of physical blocks per track in the WADS data set.

Trace record changes

The following trace subcodes are added to the IMS logger's trace. They are defined in the ILOG macro.
Table 1. New trace subcodes introduced to the IMS Logger's trace
Trace subcode Description
x'31' Completed a CONNECT request.
x'32' Completed a DISCONNECT request.
x'33' Completed a format request.
x'34' Completed writing instance ID request.
x'38' The Media Manager termination exit was driven.
x'39' The Media Manager error exit was driven.

Requirements

The support of zHyperWrite requires that both the primary and secondary data set volumes be in a Metro Mirror relationship managed by HyperSwap.

Changes to installing and defining IMS

You must define the WADS as a VSAM linear data set with a control interval (CI) size of 4 KB (4096-bytes), secondary space allocation of 0, and the SHAREOPITON (3 3) parameter.

The following JCL example demonstrates how to define 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)
/*

The installation verification program (IVP) is changed to define the WADS as linear VSAM data sets.

Changes to administering IMS

The IMS System Administrator defines all WADS to be used as VSAM linear data sets before starting the IMS 15 system for the first time.

Changes to troubleshooting for IMS

This enhancement introduces new and changed IMS messages related to Logger Media Manager.

For a list of the messages and codes that are new or changed for this enhancement, see the IMS messages and codes row in the table in Documentation changes.

For a complete list of all of the new, changed, and deleted messages, and abend codes in IMS 15, see Message and code changes in IMS 15.

Changes to utilities

Start of changeWhen IMS reads the write-ahead data sets (WADS), the Log Recovery utility might issue the DFS3253W warning message to explain the MVS messages that VSAM issues in the job log.End of change

Changes to commands

The command output of /DISPLAY OLDS shows whether zHyperWrite is used when data is written to the WADS. If zHyperWrite is enabled, WADS=YES is displayed. If zHyperWrite is not enabled, WADS=NO is displayed.

Start of changeA new keyword, ZHYPERWRITE, is added to the UPDATE IMS SET(LCLPARM) command.End of change

Documentation changes

The following table lists the publications that contain new or changed topics for the zHyperWrite support for IMS logging enhancement. Publications that are not impacted by this enhancement are not included in the table.

Table 2. Links to topics that have new or changed content for this enhancement
Publication Links to topics
Release planning Changed topics:
System definition Changed topics:
System administration Changed topics:
Diagnosis
IMS messages and codes DFS messages Abend codes
Operations and automation Changed topics:
IMS commands IMS commands