Specifying data set backup tasks

The data set backup commands allow a user to target a specific output device type. However, if an output device type is not specified, the SETSYS DSBACKUP command controls whether individual backup requests go to DASD or tape. It also allows you to define the number of tasks that are available, up to 64 tasks, to the data set backup function. The SETSYS DSBACKUP command has three parameters: DASDSELECTIONSIZE, DASD, and TAPE.

The DASDSELECTIONSIZE parameter allows you to balance the workload between DASD and tape tasks for all WAIT requests that do not target an output device. This parameter is applicable if both tape and ML1 DASD are used for data set backup requests. Defaults for this parameter are 3000 KB for the maximum size and 250 KB for the standard size. For a discussion about assigning values for maximum and standard sizes, see Assigning DASDSELECTIONSIZE values.

The DASD parameter allows you to specify the number of concurrent data set backup tasks that can direct backups to ML1 DASD. The value nn for the TASKS subparameter ranges from 0 to 64 tasks. The command can take the following form: 
SETSYS DSBACKUP(DASD(TASKS(nn)))
The TAPE parameter allows you to specify the maximum number of concurrent data set backup tasks that can direct backups to tape. The value nn for the TASKS subparameter ranges from 0 to 64 tasks. The command can take the following form: 
SETSYS DSBACKUP(TAPE(TASKS(nn)))
Note:
  1. The DASDSELECTIONSIZE parameter allows you to balance the workload between DASD and TAPE tasks for all WAIT requests that do not specify output media. By setting appropriate values, you ensure that a sufficient number of backups go to each media type to keep them busy. Ultimately, you must weigh the efficient use of data set backup tasks against media use and the need to perform a second movement of backup versions from ML1 DASD to backup tapes during automatic backup processing.
  2. The sum of both DASD and tape tasks may not exceed 64.
  3. If your installation directs a large amount of individual data set backups to tape, you may want to reassess the number of ML1 OVERFLOW volumes that you have defined to DFSMShsm.
  4. A backup to tape is a one-time process, but a backup to DASD means that the data first goes to DASD before it moves to tape. To avoid this additional data movement, it is almost always more efficient to back up to tape. (An environment with small data sets that arrive infrequently may be the exception.)

Additional TAPE subparameters are MAXIDLETASKS and DEMOUNTDELAY. The MAXIDLETASKS option allows you to tell DFSMShsm the maximum number of idle tape tasks (0 to 64) that you will accept for each delay. The DEMOUNTDELAY option allows you to tell DFSMShsm how much time to wait before it deallocates idle tape drives.

Related reading

For more information about the relationship between maximum and standard values associated with the DASDSELECTIONSIZE keyword and the SETSYS DSBACKUP command, see SETSYS command: Establishing or changing the values of DFSMShsm control parameters.

Parent topic: Using the data set backup by command capabilities