How DFSMShsm affects your recovery environment

The Data Facility Hierarchical Storage Manager (DFSMShsm) can automatically manage space and data availability among storage devices in your system. If you use DFSMShsm, you need to know that it automatically moves data to and from the Db2 databases.

Restriction: Because DFSMShsm can migrate data sets to different disk volumes, you cannot use DFSMShsm in conjunction with the BACKUP SYSTEM utility. The RECOVER utility requires that the data sets reside on the volumes where they had been at the time of the system-level backup.

DFSMShsm manages your disk space efficiently by moving data sets that have not been used recently to less-expensive storage. It also makes your data available for recovery by automatically copying new or changed data sets to tape or disk. It can delete data sets or move them to another device. Its operations occur daily, at a specified time, and they allow for keeping a data set for a predetermined period before deleting or moving it.

All DFSMShsm operations can also be performed manually.

DFSMShsm:

  • Uses cataloged data sets
  • Operates on user tables, image copies, and logs
  • Supports VSAM data sets

If a volume has a Db2 storage group specified, the volume should be recalled only to like devices of the same VOLSER as defined by CREATE or ALTER STOGROUP.

Db2 can recall user page sets that have been migrated. Whether DFSMShsm recall occurs automatically is determined by the values of the RECALL DATABASE and RECALL DELAY fields of installation panel DSNTIPO. If the value of the RECALL DATABASE field is NO, automatic recall is not performed and the page set is considered an unavailable resource. It must be recalled explicitly before it can be used by Db2. If the value of the RECALL DATABASE field is YES, DFSMShsm is invoked to recall the page sets automatically. The program waits for the recall for the amount of time that is specified by the RECALL DELAY parameter. If the recall is not completed within that time, the program receives an error message indicating that the page set is unavailable but that recall was initiated.

The deletion of DFSMShsm migrated data sets and the Db2 log retention period must be coordinated with use of the MODIFY utility. If not, you could need recovery image copies or logs that have been deleted.