Understanding DFSMShsm

DFSMShsm provides automatic management of low activity and inactive data, and automatic backup and recovery of active data in both system-managed and non-system-managed environments. DFSMShsm accomplishes this by providing the following types of management:

Automatic Storage Management

DFSMShsm is a tool that improves productivity by effectively managing storage. DFSMShsm uses a hierarchy of storage devices in its automatic management of data that relieves users from manual storage management tasks and improves DASD utilization. For more information, see Device Hierarchy.

Space Management

DFSMShsm automatically manages DASD space by enabling active data sets to be kept on fast access storage devices. DFSMShsm frees available space on user volumes by releasing over allocated space, deleting eligible data sets, and by moving low activity data sets to lower cost-per-byte devices.

By using DFSMShsm in conjunction with your automatic class selection (ACS) routines to implement the tape mount management methodology, you can write multiple output data sets to a single tape, with a single tape mount. This not only improves tape use, but also greatly reduces the number of tape mounts required by your installation.

For more information, see Managing Space.

Availability Management

DFSMShsm makes data available by automatically copying new and changed data sets to backup volumes. If the original data sets are damaged or accidentally deleted, having backup versions ensures that the data can be made available.

DFSMShsm provides the ability to back up aggregate groups of critical data sets and programs that can be taken to remote locations and used for disaster recovery or other business needs.

DFSMShsm creates and manages backup versions of storage groups defined within copy pools. DFSMShsm recovers a fast replication backup version from the volume or copy pool level.

DFSMShsm also provides the secondary host promotion function to improve data availability in instances where a DFSMShsm host processor experiences a failure in a multisystem environment. Using the secondary host promotion function, with a cross-system coupling facility (XCF) in either a basic or Parallel Sysplex® environment, a secondary host can take over the unique functions that were performed by a failed primary host. The secondary host promotion function also enables other DFSMShsm hosts to take over secondary space management functions from either a primary or secondary host that has failed. If a promoted host also fails, any remaining host that is eligible for promotion will take over.

For more information, see Managing Availability.

DFSMShsm provides a number of functions to support space and availability management. Full exploitation of DFSMShsm services in DFSMS environments requires the use of DFSMSdss for certain functions.