MAXDRIVES is originally set during the customization process and is local or subsystem specific in scope. Using the SVTn SET MAXDRIVES console command, you can adjust the setting dynamically for each CA Vtape subsystem. MAXDRIVES needs to be set for all the subsystems as either zero for Failover Backstore Engine Servers or the available number of tape drives for the Primary Backstore Engine Server.
Since this setting is controlled by a console command, CA Vtape Backstore drives usage can be adjusted as needed. If the demand for tape drives by other applications is high, Externalization can be limited by decreasing the MAXDRIVES setting to make more drives available for the other applications. Conversely, as demand by other applications decreases, Externalization can be allowed to use more drives by increasing the MAXDRIVES setting.
When FullMaxdrivesEnforcement is set to Y, the MAXDRIVES setting is checked by an Externalization task after each Virtual Volume has been copied to a Backstore Tape. When MAXDRIVES is lowered during Externalization, the first Externalization task to complete a copy will detect the change and stop, freeing its tape drives. This process continues until enough Externalization tasks have been stopped to lower the number of tape drives in use to a value equal to or less than the MAXDRIVES setting.
If MAXDRIVES is increased while Externalization is running, the next internal check for work will detect the change and start additional Externalization tasks. The change can be detected earlier if the SVTn CHECK BACKstore console command is issued to perform an immediate check for work after increasing the MAXDRIVES setting.
You can display the current setting of MAXDRIVES by using the SVTn Display Backstore and Display Groups console commands. The ISPF Interface Group Lists option also displays the MAXDRIVES setting.
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