IBM Z9, Planning Manual

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most needed. CHPIDs identified as managed in the IOCDS (via CHPARM and
IOCLUSTER keywords) are dynamically shared among z/OS images within an
LPAR cluster.
Prior to DCM, available channels had to be manually balanced across I/O devices
in an attempt to provide sufficient paths to handle the average load on every
controller. Natural variability in demand means that some controllers at times have
more I/O paths available than they need, while other controllers possibly have too
few. DCM attempts to balance responsiveness of the available channels maximizing
the utilization of installed hardware. Fewer overall channels are required because
the DCM CHPIDs are more fully utilized. RMF provides a report showing the
average aggregate utilization for all managed channels.
By using DCM, you now only have to define a minimum of one nonmanaged path
and up to seven managed paths to each control unit (although a realistic minimum
of two nonmanaged paths are recommended), with dynamic channel path
management taking responsibility for adding additional paths as required. For more
information on defining and using DCM, including detailed examples, see the z/OS
Intelligent Resource Director , SG24-5952.
IOCP Coding Specifications
ICP IOCP can only generate an LPAR IOCDS. No IOCP invocation prarameter is
required to generate an LPAR IOCDS.
IOCP Statements for ICP
The RESOURCE statement is used to specify all the logical partition names defined
in a machine configuration. To plan for growth in the number of logical partitions in
the configuration, one or more asterisks (*) may be used to specify that one or
more logical partitions are to be reserved along with their associated CSS and MIF
image IDs. A reserved LP can only be specified for a dynamic-capable IOCDS. A
dynamic-capable IOCDS is built when using HCD on z/OS or z/VM or specifying
IOCP CMS utility option DYN for z/VM. Space in the hardware system area (HSA)
is allocated for reserved LPs but cannot be used until a dynamic I/O configuration
change is made to assign a name to the LP. The following rules apply when
specifying reserved LPs:
v A reserved LP must have a user-specified MIF image ID
v
A reserved LP cannot have any channel paths assigned to it
v An IOCDS cannot contain only reserved LPs. At least one LP must be defined
with a name.
Dynamic CHPID Management (DCM) channel paths defined for a given LPAR
cluster are shareable among all active LPs that have joined that cluster. Other than
DCM channel paths, you must assign each channel path to a logical partition in an
LPAR IOCDS. For each DCM channel path, ICP requires the CHPARM keyword
have a value of 01 and the IOCLUSTER keyword on a CHPID statement. All other
channel paths require the PART|PARTITION, NOTPART, or SHARED keyword on
all CHPID statements unless a channel path is defined as spanned by specifying
multiple CSS IDs in the PATH keyword of the IOCP CHPID statement.
Use the CHPARM and IOCLUSTER keywords on the CHPID statement to specify
channel paths reserved for the use of a particular LPAR cluster. A DCM channel
path becomes available to a candidate logical partition when the LP is activated and
joins the specified cluster.
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PR/SM Planning Guide