DSBACKUP: Controlling the command data set backup environment

Explanation: DSBACKUP is an optional parameter that allows you to control the command data set backup environment. You can balance the backup workload between DASD and tape tasks and you can tailor DFSMShsm tape mounting and demounting for command data set backups. DFSMShsm can run up to 64 concurrent command data set backup tasks.

If GENVSAMCOMPNAMES(YES)|GVCN(YES) is in effect, and dsname is a VSAM base cluster and newdsname is either migrated or uncataloged, DFSMShsm will process the request, and default names will be assigned to the VSAM data and index components. If GENVSAMCOMPNAMES(NO)|GVCN(NO) is in effect, and dsname is a VSAM base cluster and newdsname is either migrated or uncataloged, the data set backup command will fail.

DASDSELECTIONSIZE (maximum␠standard) helps you balance the workload between DASD and tape tasks for all WAIT-type requests that do not target tape. DASDSELECTIONSIZE is only applicable if both tape and ML1 DASD are allowed for command data set backups. maximum is the size, in kilobytes, of the largest data set, (a WAIT-type request) that is directed to ML1 DASD. standard is the largest size, in kilobytes, that is considered to be a small data set. DFSMShsm directs small data sets (a WAIT-type request) to DASD if a tape task is not immediately available to process the request. DFSMShsm directs NOWAIT requests to tape, if tape tasks are allowed. The values that you can specify for maximum and standard range from 0 to 999999.

A data set is considered small if it is less than or equal to standard. A data set is considered large if it is greater than maximum. A data set with a value between maximum and standard is a medium data set.

To determine whether a data set uses tape or disk, refer to Table 1.

Note: The default is DASDSELECTIONSIZE(3000␠250), where 3000 is the maximum in kilobytes, and 250 is the standard in kilobytes. The categories in the table are based on these default values. If the you change the DASDSELECTIONSIZE(maximum␠standard) settings, then these categories change.

Table 1. Determining Data Set Task Targets
Default Criteria	Large	Medium	Small
Data set size	3001 KB and up	251–3000 KB	0–250 KB
WAIT-type requests	Favor tape	First available	Favor disk
NOWAIT-type requests	Favor tape	Favor tape	Favor tape

The following list describes the task targets that are used in Table 1.

This task target . . .	Means . . .
Favor disk	Small data sets that are processed by WAIT-type requests will select ML1 DASD as target. However, if you specify DASD(TASKS(0)), the data set will use tape.
Favor tape	Data set backups will be directed to tape unless you specify TAPE(TASKS(0)).
First available	Data sets will favor the first available task, regardless of disk or tape. If both tasks are available, it will favor the tape task.

Note:

If you want command data set backups to go to DASD only if targeted to do so, and all nontargeted command data set backups to go to tape, you can specify DASDSELECTIONSIZE(0 0). This forces all nontargeted command data set backups to go to tape.
If only one value is specified for DASDSELECTIONSIZE, it will be interpreted as the maximum size.

DASD(TASKS(nn)) specifies that you want to use ML1 DASD for command data set backups.

TAPE(TASKSnn) DEMOUNTDELAY(MAXIDLETASKS(drives) MINUTES(minutes))) specifies that you want to use tape for command data set backups.

You can also specify both DASD and tape for command data set backup tasks. TASKS(nn) specifies the maximum number of concurrent command data set backup tasks that DFSMShsm directs to ML1 DASD or to tape. nn is a value between 0 and 64. If the number of DASD or tape tasks specified is 0, all command data set backup requests targeting the backup to DASD or tape fail. The sum of DASD(TASKS(nn)) and TAPE(TASKS(nn)) cannot exceed 64. If the sum is zero, any request fails.

DEMOUNTDELAY allows you to tailor the DFSMShsm tape mounting and demounting for command data set backup. MINUTES(minutes) is the number of minutes that you want DFSMShsm to wait before it deallocates the tape associated with continuously inactive (idle) command data set backup tasks. minutes is a value from 0 to 1440. A value of 1440 indicates that DFSMShsm will not demount the tape until command data set backup tasks are held, a SWITCHTAPES event occurs, or DFSMShsm shuts down, so this value extends across 24 hours.

If you specify DEMOUNTDELAY(MINUTES(0)), a tape that is mounted for command data set backup remains mounted long enough to support a continuous stream of WAIT-type backup requests to tape from a single job stream even if the queue of work momentarily becomes empty.

Note: The tape will remain mounted for up to 5 seconds if MINUTES(0) is specified.

A change to the DEMOUNTDELAY(MINUTES) value results in a new delay time being set. This new time is calculated from the current time of day. In other words, the new delay does not take into account any time the tape has been idle up to the issuance of this change.

MAXIDLETASKS(drives)) is the maximum number of tape drives that DEMOUNTDELAY can accommodate. drives is a value from 0 to 64. You can specify a maximum of 64 drives for MAXIDLETASKS, regardless of the number of TAPE tasks specified. However, the effective number of tasks for MAXIDLETASKS is bound by the number of TAPE tasks. So, if you specify MAXIDLETASKS(64) and TAPE(TASKS(5)), the effective MAXIDLETASKS is 5. If at a later time you respecify TAPE(TASKS(7)), the effective MAXIDLETASKS becomes 7.

When you issue the QUERY SETSYS command, DFSMShsm displays the number of MAXIDLETASKS specified. The QUERY ACTIVE command displays both the effective number of MAXIDLETASKS and the number of current idle tape tasks (that is, drives that are allocated but have no work).

When a command data set backup task writing to tape completes, DFSMShsm does not deallocate tape units until all queued command data set backup requests have been processed. This enables all consecutive WAIT-type requests by the same batch job to be performed without going through a demount/mount sequence.

DEMOUNTDELAY notes:

DEMOUNTDELAY(MINUTES(0)) or MAXIDLETASKS(0) specifies that DFSMShsm deallocates tapes when there are no requests on the queue that the tape task could select. The tape task can select any requests except those that are restricted to DASD.
If a tape drive is idle (waiting for additional backup requests) and is then used to satisfy a command data set backup request, DFSMShsm resets the DEMOUNTDELAY time specified for that drive. In other words, the DEMOUNTDELAY is per instance, not an accumulation of idle time.

SMS relationship: Parameter has the same meaning when applied to SMS-managed or non-SMS-managed DASD volumes or data sets.

SETSYS default: None.

DFSMShsm default: If you do not specify the DASDSELECTIONSIZE parameter on any SETSYS command, the DFSMShsm default for maximum is 3000 KB, and standard is 250 KB. If you do not specify the DASD(TASKS) or TAPE(TASKS) parameters on any SETSYS command, the DFSMShsm default for nn is 2. If you do not specify DEMOUNTDELAY parameter on any SETSYS command, the DFSMShsm default for MAXIDLETASKS is 0. If idle tape tasks exist and the MINUTES parameter was not specified, then the default for MINUTES is 60 minutes.

Note:

You can prevent DFSMShsm from directing command data set backups to ML1 DASD by specifying DASD(TASKS(0)).
You can prevent DFSMShsm from directing command data set backups to tape by specifying TAPE(TASKS(0)). You should do this if daily backup targets DASD in your installation.
You can prevent nontargeted command data set backups from going to ML1 DASD by specifying DASDSELECTIONSIZE(0).
A change in TAPE(TASKS(nn)) requires DFSMShsm to start additional tape tasks or stop existing tape tasks (at the end of processing the current command data set).
If the sum of tape and DASD tasks exceed the high limit of 64, the command fails.
Use care in making a change in the DEMOUNTDELAY parameter. For instance, if a backup to tape task completes its work, the value for MAXIDLETASKS is greater than zero, and DEMOUNTDELAY(10) is in effect, DFSMShsm sets an internal timer for 10 minutes.
- If after 10 minutes, no additional work is received, the task begins to deallocate the drive and ends.
- If during this 10 minute idle time the task is selected to perform a backup, the timer is cancelled. Once the task is complete DFSMShsm again sets a timer value of 10 minutes.
- If during this 10 minute delay, the time is decreased to 5 minutes by using DEMOUNTDELAY(MINUTES(5)), DFSMShsm cancels the current timer and a new timer is established for 5 minutes (not taking into consideration any previous time).
- If DEMOUNTDELAY(MINUTES(3)) is in effect and you issue an increase such as DEMOUNTDELAY(MINUTES(10)), DFSMShsm cancels the current timer value and uses the new value. This resets the countdown to 10 minutes from the time the command is received.
If a parsing error occurs, DFSMShsm fails the SETSYS command with the ARC1605I message. For nonparsing errors but contextual errors, DFSMShsm fails the parameter in error but continues to process all other parameters in the SETSYS DSBACKUP command. DFSMShsm treats the TAPE(TASKS) and DASD(TASKS) parameters as a single entity. For example, SETSYS DSBACKUP(DASDSELECTIONSIZE(5000 300) DASD(TASKS(45)) TAPE(TASKS(20))) results in DASDSELECTIONSIZE being set, but DASD(TASKS) and TAPE(TASKS) fail because the sum of both tasks exceeds 64.