Determination of Output Data Set Location

The CTTSBD utility determines placement for output data sets in the following way:

The CTTSBD utility first attempts to place the current data set on the current output volume chain (meaning, the chain on that the previous data set was stacked).

• If the data set cannot be placed on the current volume chain, the CTTSBD utility attempts to place the data set on the first volume chain created during this run of the utility.
• If the first volume chain is not suitable, the second one is considered, and so on. The CTTSBD utility considers each chain created during this run (in the order in which they were created) as a possible location for the current data set until either a suitable volume chain is found or all chains have been considered.
• If no suitable volume chain is found, the data set is placed on a scratch volume.

Data sets can be stacked on volumes (or multi-volume chains) created during a run of the CTTSBD utility even after the volumes have been dismounted.

Each volume chain considered as a possible location for the current data set is processed in the following way:

1. The data set group definition associated with the current data set is compared with the data set group definition of each data set on the candidate volume chain.

   If a statement specified in any data set group definition does not allow the data sets to coexist in the same volume chain (due to group name, job name or data set name) the CTTSBD utility rejects the volume chain and attempts to place the data set on the next volume chain. (Data set group stacking parameters are described in detail later is this guide.)

2. The CTTSBD utility searches the data set group definitions for a WITHGRP statement that indicates that the current data set must be stacked together with the data sets on the candidate volume chain. An appropriate WITHGRP statement can exist in the data set group definition of the current data set and/or a data set on the candidate volume chain. (WITHGRP statements are described in detail later in this guide.)
   • If a matching WITHGRP statement is found, the CTTSBD utility copies the data set to the volume chain (as long as limits specified to the utility have not been exceeded).

     Note: You can maximize media utilization by instructing the CTTSBD utility to create output volume chains containing a large number of volumes (using the OUTMVLIM parameter). You can also control the number of data sets in an output volume chain using the MAXLABEL parameter. If the specified maximum number of volumes in a chain is exceeded during the writing of a multi-volume data set (for example, due to an inaccurate prediction concerning data set length) the utility CTTSBD continues writing the data set on as many volumes as required.

   • If no matching WITHGRP statement is found, the CTTSBD utility rejects the volume chain and attempts to place the data set on the next volume chain.

     Note: Exit CTTX011 (if implemented) is invoked at various stages in the above process to modify or force a stacking decision. For more information, see Exit CTTX011 and the CTTX011 member in the IOA SAMPEXIT library.