Chapter 7. Sysplex functions 179
Draft Document for Review April 7, 2004 6:15 pm 6947ch07.fm
Where several channels are attached from a z990 LCSS to a switch, they can be considered
a resource pool for accessing any of the control units attached to the same switch. To achiev e
this without DCM would require deactivating paths, performing a dynamic I/O reconfiguration,
and activating new paths. DCM achieves the equivalent process automatically, using those
same mechanisms.
Channels managed by DCM are referred to here as “managed” channels. Channels not
managed by DCM are referred to as “static” channels.
Workload Manager dynamically moves channel paths through the ESCON Director from one
I/O control unit to another in response to changes in the workload requirements. By defining a
number of channel paths as managed, they become eligible for this dynamic assignment.
By moving more bandwidth to the important work that needs it, your disk I/O resources are
used much more efficiently. This may decrease the number of channel paths you need in the
first place, and could improve availability because, in the event of a hardware failure, another
channel could be dynamically moved over to handle the work requests.
Dynamic Channel Path Management runs on a zSeries server in z/Architecture mode, in both
basic and LPAR mode. The participating z/OS system images can be defined as XCFLOCAL,
MONOPLEX, or MULTISYSTEM.
If a system image running Dynamic Channel Path Management in LPAR mode is defined as
being part of a multisystem sysplex, it also requires a CF level 9 Coupling Facility structure,
even if it is the only image currently running on the system.
Dynamic Channel Path Management operates in two modes:
򐂰Balance mode
In balance mode, DCM will attempt to equalize performance across all of the managed
control units.
򐂰Goal mode
In goal mode, which is available only when WLM is operating in goal mode on systems in
an LPAR cluster, DCM will still attempt to equalize performance, as in balance mode. In
addition, when work is failing to meet its performance goals due to I/O delays, DCM will
take additional steps to manage the channel bandwidth accordingly, so that important
work meets its goals.
Enabling Dynamic Channel Path Management involves defining managed channels and
control units via HCD. On the Hardware Management Console, you then need to ensure that
all of the appropriate logical partitions are authorized to control the I/O configuration.
For additional information on implementing Dynamic Channel Path Management under IRD
see z/OS Intelligent Resource Director, SG24-5952.
Value of Dynamic Channel Path Management
Dynamic Channel Path Management provides the following benefits:
򐂰Improved overall image performance
Improved image performance is achieved by automatic path balancing (WLM compatibility
and goal mode) and Service Policy (WLM goal mode).
򐂰Maximum utilization of installed hardware
Channels will be automatically balanced, providing opportunities to use fewer I/O paths to
service the same workload.