Recommendations

Creating I/O configuration definitions where channels could request more logical paths to control units than the control units could support can be useful in the following scenarios:

• Workload balancing

  When a system image becomes overloaded, you might need to reassign a workload and the necessary logical paths (for example, its tape or DASD volumes, a set of display terminals, or a set of printers) to another system image that has available capacity.

• Backup

  When an outage occurs, you can move the critical application set (the program and associated data) and the necessary logical paths to a backup or standby CPC. This process is simple if the CPCs have identical I/O configurations.

In I/O configurations where channels can request more logical paths to control units than the control units can support, you can manage how logical paths are established by:

• Deactivating unneeded LPs.
• Configuring offline unneeded channels. For shared channels, configure offline unneeded channels on an LP basis.
• Limiting the number of LPs that can access the I/O devices attached to a control unit when the control unit attaches to shared channels. In IOCP, specify the PARTITION or NOTPART keyword on the IODEVICE statement for every I/O device attaching to a control unit so that 1 or more LPs cannot access any of the I/O devices.
• Using the Director to block ports or prohibit dynamic connections or communication between ports.
• Combinations of the options in this list.

To better understand how you can manage logical paths using these methods, consider the following examples.