Managing The Establishment Of Logical Paths; Logical Path Considerations - IBM Z9 Planning Manual

Managing the Establishment of Logical Paths

You can manage the establishment of logical paths between channels and control
units. With proper planning, you can create I/O configuration definitions that allow
control units in the configuration to allocate logical paths for every possible request
made by channels in either of the following ways:
v Create a one-to-one correspondence between the logical path capacity of all
v Create I/O configurations that can exceed the logical path capacity of all or some

Logical Path Considerations

You can better understand how to manage the establishment of logical paths by
understanding the following:
v Control unit considerations
v Connectivity considerations
v Channel configuration considerations
v 9035 ESCON Converter considerations
Control Unit Considerations: Consider the following factors concerning the
allocation of logical paths by control units:
v Control units allocate logical paths dynamically on a first-come-first-served basis.
v Control units vary in the number of logical paths they support. See Table 2-3 on
Connectivity Considerations: ESCON and FICON system hardware, CPCs, and
ESCON and FICON Directors significantly affect the volume of logical path requests
to a control unit as follows:
v Control units can attach to one or more ports on a Director or to additional ports
v For CPCs, each logical partition attaching to the same control unit will compete
v In a configuration where control units are shared by different CPCs, I/O
v Shared channels require the establishment of a logical path for each channel
Channel Configuration Considerations: The following configuration rules
determine how logical paths are established for ESCON and FICON channels.
v A channel initially attempts to establish logical paths:
control units in the physical configuration and the channels attempting to request
them.
of the control units in the physical configuration but, at the same time, provide
the capability to selectively establish logical connectivity between control units
and channels as needed.
This capability can be useful or even necessary in several configuration
scenarios. See "Recommendations" on page 2-12.
Control units do not manage the allocation of logical paths but instead allow
channels to compete for logical paths until all of the control unit's logical paths
are used.
page 2-8.
on other Directors. Each Director port can dynamically connect to many other
ports to which channels requesting logical paths are attached.
for the control unit's logical paths.
configuration definitions for individual control units are not coordinated
automatically among the IOCDSs of the different CPCs. Each CPC competes for
a control unit's logical paths.
image corresponding to an active LP sharing the channel. This can significantly
increase the number of logical paths that a single channel requests.
Chapter 2. Planning Considerations
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