Prior to dynamic channel path management, all channel paths to I/O control units had to be statically defined. In the event of a significant shift in workload, the channel path definitions would have to be reevaluated, manually updated via HCD, and activated or PORed into the configuration. Dynamic channel path management lets workload management dynamically move 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 DASD I/O resources are used more efficiently. This may decrease the number of channel paths you need in the first place, and could improve availability — in the event of a hardware failure, another channel could be dynamically moved over to handle the work requests.
Dynamic channel path management operates in two modes: balance mode and goal mode. In balance mode, dynamic channel path management will attempt to equalize performance across all of the managed control units. In goal mode, which is available only when WLM is operating in goal mode on all systems in an LPAR cluster, WLM 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, WLM will take additional steps to manage the channel bandwidth accordingly, so that important work meets its goals.
Dynamic channel path management requires z/OS® and a zSeries server in z/Architecture® mode, running in either basic mode or LPAR mode. 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 CFLEVEL 9 coupling facility structure, even if it is the only image currently running on the CPC.