Utilizing standby mode

To activate a console, you typically must issue a VARY command from another console. If another console is not available and you are activating an HMCS console, you also have the option of accessing the HMC and attaching the Integrated 3270 icon to the LPAR icon. After pressing the attention key, the console is active. These console activation methods consume system services and resources such as storage, queues, CPU cycles, and lock usage, many of which are potentially unavailable during emergency situations. To reduce the amount of system services and resources that are used, and to better prepare for emergency situations, consider placing consoles that you are not actively using in standby instead of inactive mode.

Standby mode is available for HMCS and MCS display consoles in full capability (FC) mode. SMCS, EMCS, subsystem consoles, the system console, printer consoles, and consoles in status display (SD) or message stream (MS) mode are not supported.

When a console is in standby mode, z/OS no longer processes I/O on it. However, the console has already undergone the open process, and ENQs and control blocks that represent the console are already obtained. So, the overhead that is required to switch the console back into active mode is greatly reduced, which is especially beneficial during critical situations.

Note: Consoles cannot initialize in standby mode because the open process requires an online device. You must activate a console before switching it to standby mode.

The SUPSBY option on the CONSOLE statement designates whether a specified console should support standby mode. If the console is not eligible for standby mode, N/A will display. After a console is set to support standby mode, you can use various methods to switch it between active and standby modes.

Switch from active mode to standby mode

Use either of the following two methods to switch your console from active mode to standby mode:

Drop the session.
Issue the VARY CN(name),STANDBY command

Switch from standby mode to active mode

Use either of the following two methods to switch your console from standby mode to active mode:

Press an attention key such as enter or PA1.
Issue the VARY CN(name),ONLINE command.

Note: If the console requires authentication, you must log on again after the console is reactivated.

When running in distributed mode, consoles in standby mode count toward the limit of 99 active consoles per system. When running in shared mode, consoles in standby mode count toward the limit of 99 defined consoles per sysplex.

Standby support is similar to the Open Systems Adapter (OSA) Express Integrated Console Controller (ICC) feature on MCS consoles called "Defer Host Disconnect" (DHD). However, when implementing DHD, z/OS continues to process I/O on the console while the session is disconnected. OSA just claims that the I/O was successful. Using the standby mode instead is an efficient choice because, with standby, no I/O goes to the console and fewer system resources are utilized.