Enabling dynamic channel path management

When using dynamic channel path management, your CPC can be running in either basic or LPAR mode. In basic mode, a coupling facility structure is not needed as there will be no logical partitions grouped together in an LPAR cluster. In LPAR mode, a coupling facility structure 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 system image is the only member of that sysplex on this CPC). You do not need a coupling facility structure if all the logical partitions are running in XCFLOCAL or MONOPLEX mode.

The IBM® Redbook, z/OS® Intelligent Resource Director (SG24-5952), provides extensive guidance on choosing the appropriate channels and control units for dynamic channel path management. Once you have selected them, there are two specific HCD definitions that will need to be changed:

Channel definitions
When defining (or modifying) a channel, you must specify YES in the Managed field. You must also specify a dynamic switch (in this case, the ESCON® Director) to which the channel is attached. You should 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 sysplex 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. You must also define this channel as 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.

Note: Ensure that each LPAR cluster name (the sysplex name that is associated with the LPAR cluster) is uniquely named across the entire CPC. As managed channels have an affinity to a specific LPAR cluster, non-unique names would create problems with the scope of control.
Control unit definitions
Whereas non-managed channel paths (otherwise called static channel paths) are defined in the traditional way, via the CHPID number, a managed path is defined by specifying a double asterisk (**). The number of double asterisks you specify will limit the number of managed channel paths per LPAR cluster. The total number of non-managed and managed channel paths, per CPC, cannot exceed 8.

Important: You must define at least one non-managed channel path (which must be defined as shared) per control unit.

The control unit must be attached to a switch (again, in this case an ESCON Director) which in turn must be attached to managed channels.

After changing the HCD definitions, the remaining actions to enable dynamic channel path management occur in the Primary Support Element Workplace, as follows:

For basic mode or LPAR mode, ensure that the CPC's reset profile is enabled for dynamic I/O.
For an LPAR cluster environment, ensure that all partitions in the cluster are authorized to control the I/O configuration.
Ensure that the automatic input/output (I/O) interface reset option is enabled in the CPC's reset profile. This will allow dynamic channel path management to continue functioning in the event that one participating system image fails.

If you wish to disable dynamic channel path management, issue the SETIOS DCM=OFF command. The SETIOS DCM=ON command will turn it back on. Issue the SETIOS DCM=REFRESH command to refresh the control unit model table (for instance, to include a new IOSTnnn load module provided by the control unit's manufacturer).

Note: After issuing the SETIOS DCM=OFF command, your I/O configuration might now be unable to handle your workload needs, as it will now be in whatever state dynamic channel path management left it before being disabled. You might need to activate a new I/O configuration that will meet your workload needs across the entire LPAR cluster.