An integral part of Intelligent Resource Director (IRD), introduced in z/OS® Release 1, 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 ESCON® 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, available only when WLM is running 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, available whether WLM is running in goal mode or compatibility mode, dynamic channel path management will simply attempt to balance the responsiveness of all the DASD subsystems, moving dynamic channels as needed.
Dynamic channel path management is allowed only on an IBM® 2064 (IBM zSeries 900) or later CPC. HCD ensures that no managed channel paths are connected to a CPC prior to this level.
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. To use dynamic channel path management, the CPC can be running in either basic or LPAR mode. In basic mode, a coupling facility is not needed, as there will be no logical partitions grouped together in an LPAR cluster. 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 CPC (or 256 per logical channel subsystem on an IBM zSeries 890 or later processor)
- 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 ESCON 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.
If you are running in LPAR mode, 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 CPC (or managed channel paths per logical channel subsystem on an IBM zSeries 890 or later processor). The total number of non-managed and managed channel paths per CPC (or managed channel paths per logical channel subsystem) cannot exceed 8. On an IBM zSeries 890 or later processor, 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 (in this case, an ESCON director) which in turn must be attached to managed channels.
See the z/OS HCD User's Guide for more information on using these panels to define managed channels and control units.