Dynamic system interchange (DSI)

Dynamic system interchange (DSI) is the backup facility to be used if a permanent machine or program failure occurs on the global or if system reconfiguration is necessary for preventive maintenance. If you cannot perform an IPL on the global or restart the JES3 global address space if an IPL is not required within a reasonable period of time, DSI allows JES3 to continue operation by switching the global function to a local main in the same JES3 complex. If a failure occurs during DSI, try a hot start. A failure during connect processing could be the cause of the failure. If the failure recurs, a warm start is required.

The DSI procedure consists of a sequence of commands (entered on either the old or the new global) and messages described below. (See z/OS JES3 Messages for detailed descriptions of and responses to messages.)

The commands used during the DSI procedure are:


>>-+-*CALL-+--,--DSI-------------------------------------------><
   '-*X----'


>>-+-*START-+--,--DSI------------------------------------------><
   '-*S-----'


>>-+-*CANCEL-+--,--DSI-----------------------------------------><
   '-*C------'

It is important to ensure that the old global's JES3 address space is no longer functioning when the new global is being initialized during the DSI process. This includes the JES3DLOG address space that might have been executing on the global z/OS® system as well. By following the step-by-step procedures for DSI in Table 1, this will be accomplished. Not all messages received are shown. Only the key messages are shown along with comments as to why they are important.

Unless the console where you entered these commands receives messages that are issued with a routing code of 10 or its equivalent destination class, you might not receive messages related to DSI. To determine whether a console is receiving route code 10, use the MVS™ command D CONSOLES. If a console is not receiving routing code 10, the routing code can be added through the use of the MVS command VARY CN( ) with the AROUT parameter. See z/OS MVS System Commands for more information about the D CONSOLES and VARY CN( ) commands.

Your system programmer should have a DSI procedure tailored to your installation and update it to reflect any changes in the complex's configuration. The chart below outlines the basic sequence of the DSI procedure; but an installation should have its own DSI procedure before attempting a DSI.

There are three scenarios that are possible during a DSI procedure. If the global processor has lost communication in the sysplex, then XCF signaling messages (for example, IXC402D, "LAST OPERATIVE AT hh:mm:ss. REPLY DOWN AFTER SYSTEM RESET OR INTERVAL=SSSSS TO SET A REPROMPT TIME") might be issued on one of the JES3 locals. Before entering the DSI procedure, consider correcting the situation that led to the XCF messages, if possible, so that a DSI need not be done.

If a DSI is required, start the DSI procedure by calling the DSI DSP on the new global. During this procedure, message IAT0910 will eventually appear indicating the old global (both the JES3 address space and the JES3DLOG address space) must no longer be active. By following the appropriate procedures, you will ensure that this is accomplished.

Table 1 identifies which commands and messages are applicable to the these three scenarios:

Scenario 1: The old global's processor has completely failed; both JES3 and MVS are no longer active.
All commands are issued from the new global as operator interaction with the old global is not possible in this case.

XCF status monitoring messages might or might not be present on the new global, and your procedure will vary depending on any outstanding messages to which you need to reply. Table 1 indicates some of these messages.
Scenario 2: Both JES3 and MVS on the old global are still active, available, and continue to perform work. However, you might want to perform a DSI to a new global for other installation-specific reasons. For example, you might just want to test your local DSI procedures.
In this case, commands for the DSI process will be issued on both the old and the new global to ensure that all JES3 components (both the JES3 global address space and the DLOG facility of JES3) are ended normally on the old global before the DSI to the new global is attempted. To ensure proper termination of JES3 on the old global, the correct JES3 commands (as shown) must be used.
Scenario 3: The JES3 address space on the old global has failed and is now inactive, but MVS is still active.
Note that DLOG (the optional recorder of all communication in the complex, both commands and messages) must be made inactive on the old global before the new global initializing during the DSI process. DLOG consists of a separate system address space (JES3DLOG) on the JES3 global processor. It is initialized either by the *MODIFY,O,DLOG=ON operator command or through a JES3 initialization stream statement setting (DLOG=ON on the CONSTD statement). If DLOG is still executing on a different MVS system when the new global initializes, incorrect processing will occur. Therefore, this scenario requires the operator to cancel the JES3DLOG address space.

Table 1. DSI Processes
Console/Processor	Command/Message	Action/Response
All Scenarios:
Inform the local processor that it is about to become the new global.
new	8X,DSI	Notifies JES3 that a DSI is going to be done. This command can be issued when a DSI procedure is to be invoked. It can be issued after the IXC402D message above appears or it can be invoked without other messages preceding this command to have the operator initiate the DSI procedure. Important: The correct command prefix character that is system-scoped (remains on the new global system and is not automatically transported to the old global) must be used. In many installations, "8" is the character that is used. If the global processor is still active, use of the syntax-wide scoped prefix character, typically "*", would incorrectly route the command to the global, regardless of where issued in the complex. See your installation's JES3 initialization stream or system programmer for the correct system-scoped prefix for your installation.
new	IAT0915	DSI - REVIEW LOCAL DSI PROCEDURE FOR main. Review your installation's guidelines for DSI.
new	8S,DSI or 8C,DSI	Use the 8S command to continue with DSI, or the 8C command to end DSI.
new	IAT0910	DSI - DISABLE OLD GLOBAL. Note: If the global is already disabled, message IAT0910 will not be issued. You can now enter C,DSI to end the DSI or follow one of the below steps to disable the old global. If you proceed with disabling the old global, JES3 will automatically detect when you have done so and proceed to the next step. You need not issue the S,DSI command at this point. Attention: It is extremely important that you end both JES3 and the JES3DLOG address space on the old global. JES3 spool integrity can be destroyed or JES3 initialization will fail for the new global, or both. These procedures ensure that JES3 and JES3 DLOG will terminate.
Proceed to one of the following steps to disable the old global for the specific scenario for which you are performing a DSI.
To Disable a Failed Global - Scenario 1 (JES3 inactive, MVS inactive):
old	RESET	Perform a system reset (optional) on the old global.
new	IXC402D	LAST OPERATIVE AT hh:mm:ss. REPLY DOWN AFTER SYSTEM RESET OR INTERVAL=SSSSS TO SET A REPROMPT TIME. XCF messages might or might not be outstanding on the new global. If they are: Reply: R nn,DOWN (or reply to IXC409D below).
new	IXC409D	SIGNAL PATHS BETWEEN new AND old ARE LOST. REPLY RETRY OR SYSNAME=SYSNAME OF THE SYSTEM TO BE REMOVED. Reply: R nn,SYSNAME=old where old is the name of the old global or reply to IXC402D above if it is outstanding; either one will continue the process if both messages are outstanding.
new	IXC417D	CONFIRM REQUEST TO REMOVE old FROM THE SYSPLEX. REPLY SYSNAME=old TO REMOVE old OR C TO CANCEL. Reply: R nn,SYSNAME=old where old is the name of the old global. (The message occurs if the operator responded to IXC409D above.)
new	IXC102A	XCF IS WAITING FOR SYSTEM old DEACTIVATION. REPLY DOWN WHEN MVS ON old IS DOWN. Reply: R nn,DOWN (The message might not occur if you responded to message IXC402D rather than to message IXC409D.)
new	IXC105I	SYSPLEX PARTITIONING HAS COMPLETED FOR old. This is an informational message indicating the old global has been removed from the sysplex by XCF.
Proceed to "After the Old Global has been Disabled."
To Disable an Active Global - Scenario 2 (JES3 active, MVS active):
		Note: Do not use RETURN to disable an active old global. The X DSI sequence should be used to ensure that the JES3DLOG address space, if active, is disabled on the old global before initializing the new global.
old	*X,DSI	Notifies the old global that it is about to be disabled.
old	IAT0920	DSI - CHECK GLOBAL DSI PROCEDURE FOR main Review your installation's guidelines before disabling the old global. Note: If this message does not appear, the old global is not active. Follow the procedure for a failed global, beginning with RESET.
old	S,DSI or C,DSI	IAT0905 DSI - STARTED FOR old.
Proceed to "After the Old Global Has Been Disabled."
To Disable an Active Global - Scenario 3 (JES3 inactive, MVS active):
old	FORCE JES3DLOG, ARM	IAT7123 DLOG ADDRESS SPACE FAILED IEE301I JES3DLOG FORCE ARM COMMAND ACCEPTED The JES3DLOG address space is canceled on the old global. This is performed so that when JES3 is brought up on the new global and attempts to initialize the JES3 complex-wide JES3DLOG address space, if needed, the existing JES3DLOG will have been terminated.
old	IAT0921	DSI - WARNING: SYSTEM ssssssss HAS nnnnn ACTIVE NETSERV(S) This message is issued if there is a processor in the complex that is running a JES3 release below z/OS V1R8 and there is at least one Netserv running somewhere in the JES3 complex. You can ignore this message if the intended new global is running z/OS V1R8 JES3 or higher. If the new global is down level, you must bring all active Netservs in the complex down before you enter the *S,DSI command to disable the old global.
Proceed to "After the Old Global Has Been Disabled."
After the Old Global Has Been Disabled - All Scenarios Rejoin Here (all three scenarios above join this common procedure to start the new global at this point):
new	IAT7124	DLOG IS NOW INACTIVE The JES3DLOG address space is no longer active. You can now safely continue the DSI on the new global.
new	IAT0900	DSI - SWITCH GLOBAL DEVICES Switch all JES3 devices, all RJP or networking communications lines, and any other equipment that must be on the global to the new global. (Check your installation's procedures; switching can involve a 3814 or similar switching device.) Note: These devices have to be varied on-line to MVS on the new global; use the MVS command V ([ddd][,ddd]...),ONLINE.
new	8S,DSI or 8C,DSI	Use the 8S command to continue with DSI or the 8C command to end DSI. Note: This is the last opportunity to cancel DSI.
new	IAT0905	DSI - STARTED From this point on, proceed as for a regular hot start.
new	*S,main,FLUSH	If you do not expect to re-IPL and start JES3 on the old global processor immediately after a DSI, you must issue the *S,main,FLUSH command. This is to: ensure that jobs registered with automatic restart manager on the old global processor are restarted on either the new global processor or on another active local processor. tell the new global, all work in an on-main state, on the specified main, is to be removed from that state. This will allow JES3 to apply the failure option to all batch jobs and also allow the restarting of FSSs on the new global or another active local processor if the FSS is defined to execute there.