Distributed mode

Distributed mode is a new mode of console operation. Distributed mode improves the operation of z/OS® console support when running in a sysplex environment by:

Potentially reducing the time that it takes to IPL a system
Potentially reducing the time that it takes a system to join a sysplex ¹
Potentially reducing the scope of console related hangs ²
Reducing the possibility of consoles related outages
Allowing more MCS, SMCS and subsystem consoles to be configured

Many of the improvements present in distributed mode are due to changes in the serialization of console resources. In some cases, synchronization requirements have been relaxed, allowing less stringent serialization mechanisms to be used. In other cases, where strict serialization is still required, the serialization has been made much more granular so that the effects of the serialization are less widespread. The relaxed synchronization and more granular serialization allow much more parallel activity to occur, reducing the time required to perform some operations. The relaxed synchronization and more granular serialization reduce the possibility that a problem occurring in one place will propagate to another place (so-called "sympathy sickness").

Distributed mode defines many of the console data structures in a data space where they are accessible only through controlled, well-defined services, drastically reducing the possibility that an errant program can damage the data structures and cause an outage. All of the new distributed mode programming includes robust new error handling and recovery capabilities.

Distributed mode relieves the 99 MCS, SMCS and subsystem console per sysplex constraint by allowing up to 99 MCS, SMCS and subsystem consoles to be active per z/OS image. Additional flexibility is provided by allowing up to 250 MCS, SMCS and subsystem consoles to be defined per z/OS image (of which up to 99 may be concurrently active on that image). The number of MCS, SMCS and subsystem consoles that may be concurrently active in a sysplex is now a function of the 99 active console limit of each image multiplied by the number of z/OS images in the sysplex.

To take advantage of distributed mode, you must perform a sysplex-wide migration to distributed mode. You can do so through a sysplex-wide IPL or dynamically, while you are running. To perform the migration, all of your systems must be at the z/OS V1R10 level or higher.

The ability to fallback dynamically to the shared mode of operation is also provided. However, the fallback is potentially disruptive to your operations. See Migration and fallback considerations.

IPL option: IEASYSxx and IPL prompt CON= parameter:

CON=(…,DISTRIBUTED) to operate in DISTRIBUTED mode
CON=(…,SHARED) to continue to operate in SHARED mode

DISTRIBUTED mode is now the default.

Dynamic ("on the fly"): SETCON MODE= command:

SETCON MODE=DISTRIBUTED to migrate forward
SETCON MODE=SHARED to fallback

The ability to fallback to SHARED mode will be removed in a future release when it is no longer possible to IPL into and operate in SHARED mode.

You can determine the current console operation mode at any time by using the DISPLAY OPDATA,MODE command.

¹ Reductions in the time that it takes to IPL a system or in the time that it takes a system to join a sysplex are a function of the size of the console configuration, with the most benefit being expected in large console configurations.

² Installations must ensure that there are redundant consoles defined and active.