SETNAME Initialization Statement

The JES3 MDS algorithm uses the information specified on the SETNAME statement when searching for the proper device to be allocated for a DD request.

If a DD request is to be handled by JES3, the value (excluding the specific device number) specified in the UNIT parameter of the DD statement must also be specified in the NAMES parameter of the SETNAME statement. If the request specifies a device number in the UNIT parameter, the device number must also be specified in the XUNIT parameter of the DEVICE statement.

By specifying the same names in a different order for the same XTYPE, it is possible to create a preference order of device selection for requests requiring volume mounting. This preference might be to achieve channel path separation, if possible, while still allowing this job to run if separation cannot be achieved.

Devices with Three Channel Paths

    DEVICE,XTYPE=(3330CH1,DA),XUNIT=(130,SY2,S1,ON)
    DEVICE,XTYPE=(3330CH2,DA),XUNIT=(230,SY2,S1,ON)
    DEVICE,XTYPE=(3330CH3,DA),XUNIT=(330,SY2,S1,ON)
    SETNAME,XTYPE=3330CH1,NAMES=(DACH1,DISK1)
    SETNAME,XTYPE=3330CH2,NAMES=(DACH1,DACH2,DISK2)
    SETNAME,XTYPE=3330CH3,NAMES=(DACH1,DACH2,DACH3,DISK3)
    SETNAME,XTYPE=3330CH1,NAMES=(DACH2,DACH3)
    SETNAME,XTYPE=3330CH2,NAMES=(DACH3)

Requests for DACH1 would attempt allocation on channel path 1, then channel path 2, and finally on channel path 3. Similarly, requests for DACH2 would attempt allocation first on channel path 2, then channel path 3, then channel path 1. By using DISK1, DISK2, or DISK3, strict channel path separation could be achieved.

Although a name may appear in more than one SETNAME statement, all XTYPE parameters applying to the name must be the same type (all DA for example). All names on the SETNAME statement must be defined to MVS™.

The maximum number of unique names specified on the SETNAME statement must not exceed 255. Each XTYPE should be defined to allow JES3 allocation to reference as large a collection of devices as possible to minimize the number of name/unit references that need to be examined by the JES3 allocation algorithm. The most frequently referenced names should be specified first (DASD, then tape, unit-record, and graphic devices).

The POOLNAMS parameter is provided to allow a convenient method of dedicating specific devices, even though there is no specific generic or esoteric name subset that exactly describes the attributes to be used to choose a specific set of devices. These names are allowed to be used only to dedicate devices and may not be used in the DD statement UNIT parameter.

To allow the use of devices outside of MDS control, define MVS names to include the required devices and then omit these names from the SETNAME initialization statement.