IBM Z9 Planning Manual page 67

v Workload balancing
When a system image becomes overloaded, you may 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.
v 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:
v Deactivating unneeded LPs.
v Configuring offline unneeded channels. For shared channels, configure offline
unneeded channels on an LP basis.
v 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.
v Using the Director to block ports or prohibit dynamic connections or
communication between ports.
v Combinations of the above.
To better understand how you can manage logical paths using these methods,
consider the following examples.
Deactivating Unneeded Logical Partitions: Deactivating unneeded LPs can
prove useful for managing how logical paths are established on CPCs in some
situations.
The system establishes logical paths only when an LP is activated. Deactivating an
LP results in removal of those logical paths associated with the LP. This can greatly
reduce the number of logical paths requested by the system at any given time.
In Figure 2-3 on page 2-14, if all five of the LPs each share all four of the ESCON
channels and all of the LPs are activated, the 3990 would be requested to establish
five logical paths for each of the four shared ESCON channels (or a total of 20
logical paths). Because the 3990-3 only supports 16 logical paths, you will need to
manage how logical paths are established to help ensure the I/O connectivity you
require.
For example, if you used LP4 and LP5 as test LPs that did not need to be active
concurrently, you could reduce the number of logical paths requested by four by not
activating either LP4 or LP5. In this case, four LPs (LP1, LP2, LP3, and LP4 or
LP5) configured to four shared ESCON channels would request a total of 16 logical
paths. Later, you could transfer logical paths between LP4 and LP5 by first
deactivating one LP to remove its logical paths, then activating the other LP to use
the freed logical paths.
Chapter 2. Planning Considerations
2-13