The dynamic exit service is described under CSVDYNEX in z/OS MVS Programming: Authorized Assembler Services Reference ALE-DYN. It allows you to define multiple exit routines simultaneously to one exit.

Customers use their tape management system as a repository for movement rules of tape data sets to vaults or backup centers. In the allocation process, with a system-managed tape library, and especially with a VTS, the choice of a storage group needs to be influenced by whether or not the tape stays in the computing center or goes outside. For environments with multiple system-managed tape libraries and complex vaulting requirements, allocation to a particular library or VTS should be matched to the vaulting requirements of the data sets being allocated. Because this information is already available within the tape management system, this exit provides a way to make this information accessible to the ACS routines.

Allowing the tape management system's logic to more directly support tape allocation under SMS will avoid redundancy and duplication of effort. These same variables can also replace most of the filter lists currently used by customers using the IBM Tape Mount Management methodology. Though the pre-ACS routine exit is not limited to the usage described here, this is one of the ways in which this exit may be used by a tape management system.

If installation exit module IGDACSXT abends, SMS ignores the exit call and continues processing.