BS2000 knows two procedures for selecting tape devices:
Selection of a suitable tape device in the order of generation.
If multiple tape devices are in use at the same time, this can result in unfavorable load balancing. In an ETERNUS CS, for example, a number of devices connected to an ICP (Integrated Channel Processor) can be in use, while at the same time no devices are active on other ICPs.Optimized device allocation for ETERNUS CS .
The device management counts the number of active devices for each ICP and takes this counter into account for device allocation.
The optimized device allocation is set using/MODIFY-MOUNT-PARAMETER NEXT-TAPE-MOUNT=*BY-CONTROLLER.
However, in both cases the device management knows only the device reservations within a native system or within a BS2000 guest system under VM2000.
Optimized device allocation with DDAL
In native mode the BS2000 device management implements optimized device selection for ETERNUS CS independently of DDAL.
In VM2000 mode on /390 servers the DDAL (Dynamic Device Allocation) function implements optimized device allocation for ETERNUS CS over all BS2000 guest systems of a server.
To permit this, IORM must be started on the monitor system and on all BS2000 guest systems, and the DDAL function must be activated using DDAL_SET_ON=YES.
Internal communication ensures that IORM knows the allocation of the ICPs in all BS2000 guest systems of the server. When a device is allocated, IORM makes the global allocation counters available to the local device management.
Activating and deactivating DDAL
DDAL_SET_ON activates or deactivates DDAL. The current setting can also be queried.
DDAL_SET_ON |
DDAL_SET_ON=YES DDAL_SET_ON=NO DDAL_SET_ON? |
YES | DDAL is activated. In VM mode this setting is required on all guest systems on which DDAL is to be active. |
NO | DDAL is deactivated on the system. In VM2000 operation this setting is required on all guest systems on which DDAL should not be active. |
? | The current setting is queried. |