Explanation: STACK | NOSTACK is an optional parameter used to override the SETSYS ABARSTAPES setting.
STACK specifies that DFSMShsm will stack the ABACKUP output files onto a minimum number of tape volumes during ABACKUP processing.
NOSTACK specifies that DFSMShsm will not stack the ABACKUP output files during ABACKUP processing.
Defaults: This parameter defaults to the setting specified on the SETSYS ABARSTAPES command. If SETSYS ABARSTAPES was not specified, then this parameter defaults to STACK.