IBM Z9 Planning Manual page 70

Defining Devices to a Subset of Logical Partitions: You can limit I/O device
access from LPs to I/O devices assigned to shared channels by using IOCP or
HCD to specify device candidate lists. By defining devices attached to a control unit
to a subset of LPs, you can manage which LPs will attempt to establish logical
paths to the control unit through a shared channel.
If you define no devices to a control unit from a particular LP, the shared channel
associated with the LP will not attempt to establish a logical path. However, if there
is at least one device defined to the control unit for the shared channel associated
with a particular LP, the shared channel for the LP will attempt to establish a logical
path to the control unit for the LP.
In Figure 2-5 on page 2-17, LP access to a series of 3174s is managed through
use of the device candidate lists for the I/O devices attached to the control units.
The shared ESCON channel will attempt to establish only one logical path to each
of the 3174s even though 5 LPs share the channel. This is useful because the 3174
in non-SNA mode only supports one logical path.
In the example, the channel only attempts to establish a logical path for LP1 to the
3174 defined as control unit 10 because only LP1 has a device defined to that
control unit. Similarly, only LP2 can access the 3174 defined as control unit 11, only
LP3 can access the 3174 defined as control unit 12, only LP4 can access the 3174
defined as control unit 13, and only LP5 can access the 3174 defined as control
unit 14.
Partial IOCP Deck for the Configuration: The following is a partial IOCP deck for
the example in Figure 2-5 on page 2-17.
CHPID PATH=30,SHARED
CNTLUNIT CUNUMBR=10,PATH=30
IODEVICE ADDRESS=VVVV,CUNUMBR=10,PART=LP1
CNTLUNIT CUNUMBR=11,PATH=30
IODEVICE ADDRESS=VVVV,CUNUMBR=11,PART=LP2
CNTLUNIT CUNUMBR=12,PATH=30
IODEVICE ADDRESS=VVVV,CUNUMBR=12,PART=LP3
CNTLUNIT CUNUMBR=13,PATH=30
IODEVICE ADDRESS=VVVV,CUNUMBR=13,PART=LP4
CNTLUNIT CUNUMBR=14,PATH=30
IODEVICE ADDRESS=VVVV,CUNUMBR=14,PART=LP5
2-16
PR/SM Planning Guide