Defining dynamically managed channel paths
An integral part of Intelligent Resource Director (IRD) is dynamic channel path management. Instead of defining a fixed number of channel paths to control units, this function lets Workload Management (WLM) move channel paths through the FICON switch director from one 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.
Dynamic channel path management works in two modes: goal mode and balance mode. In goal mode, dynamic channel path management will manage the channel paths to best meet the performance goals of the most important work, even at the expense of less important work, if necessary. In balance mode, dynamic channel path management will simply attempt to balance the responsiveness of all the DASD subsystems, moving dynamic channels as needed.
IRD allows an installation to group logical partitions that are resident on the same physical server, and in the same sysplex, into an LPAR cluster. This gives Workload Management the ability to manage resources, both processor and DASD I/O, not just in one single image but across the entire cluster of logical partitions. In LPAR mode, a coupling facility is required if you wish to use dynamic channel path management in any logical partition containing a system that is a member of a multisystem complex (even if the logical partition is the only member of that sysplex on this CPC). You do not need a coupling facility if all the logical partitions are running in XCFLOCAL or MONOPLEX mode.
- Installations approaching the 256 channel limit per logical channel subsystem.
- Smaller installations that do not have sufficient technical resources to design and monitor DASD subsystems
- Installations that experience large variations in channel utilization at different times of day
- Installations where the highest possible availability is an absolute requirement
- Installations with a large number of control units, and multiple control units, per channel
- Installations with a large number of EMIF channels.
After you have selected the appropriate channels and control units for dynamic channel path management, there are two HCD definitions that will need to be changed: the channel definitions and the control unit definitions.
To define a channel as being managed, you must specify YES in the Managed field on the “Add Channel Path” HCD panel. You must also specify a dynamic switch (in this case, the FICON director) to which the channel is attached. It is recommended that you also specify the entry switch ID and entry port so that HCD can do consistency checking.
You must also define the name of the LPAR cluster to which a logical partition must belong in order to have this channel in its configuration. Specify this name in the “I/O Cluster” field. Finally, you must also define this channel as being shared. Note that unlike traditional shared channels which potentially can be shared by all logical partitions on a CPC, managed channels can only be shared by logical partitions in the same LPAR cluster.
To define a control unit as managed, you must make changes to its definition in the “Add Control Unit” HCD panel. Whereas non-managed channel paths (otherwise called static channel paths) are defined through the CHPID number, a managed path is defined by specifying an asterisk (*). The number of asterisks you specify will limit the number of managed channel paths per logical channel subsystem. The total number of non-managed and managed channel paths per logical channel subsystem cannot exceed 8. You must define the managed channel paths to the control unit in each logical channel subsystem.
The control unit must be attached to a switch which in turn must be attached to managed channels.
See the z/OS HCD User's Guide for more information on how to define managed channels and control units.