Defining the offload facility

Spool offload uses the order and format of NJE records and BSAM (Basic Sequential Access Method) processing to perform I/O to either tape or DASD data sets. Transmitter and receiver logical devices act as a connection between the spool and the offload data set, passing noncompressed data back and forth. JES2 allows more than one transmit or receive operation active at a time. Be certain to protect offloaded data by defining the offload data set to RACF®. During the offload process RACF ensures that the owner of the SYSOUT data has access to the offload device and on reload ensures that the proper data is reloaded before writing it to spool. You must ensure that your local node is defined to RACF, so that your SYSOUT is reloaded with the proper userid. For more information, see Protecting SPOOL offload data sets.

The OFFLOAD(n) statement defines the logical offload device that is associated with the offload data set(s). Jobs and SYSOUT are transmitted to and from a data set specified by the DSN= parameter of the OFFLOAD(n) statement. You must specify this initialization statement to use the spool offload facility. This statement is numbered to correspond to the offload transmitter statements. You can define up to eight offload devices per system by the OFFLOAD(n) statement. However, only eight offload devices can be active within a multi-access spool complex at a time. An offload device started on one member of a multi-access spool complex cannot also be started at a second member. If you attempt to do so, JES2 issues the $HASP593 message, indicating that the start has been rejected because the device is already in use.

The statements listed previously collectively control the transmitting and receiving of offload data. If you do not include transmitter and receiver statements following the OFFLOAD(n) statement, JES2 creates them for you. That is, JES2 provides four default statements: a job transmitter, a job receiver, a SYSOUT transmitter, and a SYSOUT receiver. JES2 provides default parameters values, but does not set any parameters that do not have defaults.

To control the transmission of jobs and SYSOUT that you intend to offload, use the OFF(n).JT and OFF(n).ST initialization statements respectively. For example, the statement parameters can control the transmitting of only specific classes, range of jobs, processing mode, or routecode. (See z/OS JES2 Initialization and Tuning Reference for a more complete description of each statement.)

To control the receiving of offloaded jobs and SYSOUT, use the OFF(n).JR and OFF(n).SR initialization statements respectively. As with job and SYSOUT transmitters, see z/OS JES2 Initialization and Tuning Reference for a complete description of what work selection criteria you can control.