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During New Day Processing, the CTTSTK utility reads the Trace file and gathers statistical information about data sets with non-specific retention (meaning, retention types CYCLES, CATALOG and LAST ACCESS). Based on this information, the average life span of each data set of this type is calculated and stored in the Stacking Database (STK).
Stacking of data sets with non-specific retention is performed according to installation parameter STKMODE. If STKMODE is set to R or A, the Dynamic Stacking facility calculates the expected retention date of the data set based on average data set life span. The data set is then stacked as if a specific retention was specified for it (meaning, it can be stacked on volumes that contain data sets with a specific retention type).
If STKMODE is set to S, the average data set life span is not considered and the stacking algorithm is not changed.
If a stacking statistics record is not found for a data set, that data set is treated as having an unknown retention, and the data set cannot be stacked unless installation parameter STKMODE is set to S.
Note: Prior to version 5.1.4, any data set with a nonspecific retention type was not eligible for stacking. For information about the calculated life span of a data set, see the CTTSTK utility in the INCONTROL for z/OS Utilities Guide.
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