With SMS and system-managed tape, you can manage your tape volumes and drives by using ISMF to define one or more automated tape libraries or manual tape libraries. These definitions, along with other SMS constructs and ACS routines, enable you to manage your tape environment more effectively. A tape library is a named set of related tape volumes and the set of tape drives where those volumes are mounted. You can associate each tape library with one or more tape storage groups to direct a new allocation request to a specific set of tape libraries. Existing tape data sets are allocated to tape devices within the library in which the volume resides. Associating tape volumes with a tape library ensures that SMS mounts tape volumes on tape devices that belong to that tape library.