DFSMSdfp: Adjust parameters to control whether offline device discovery is performed during IPL

Description: Beginning in APAR OA43706 (PTFs: UA74649 for z/OS V2R1, UA74648 for z/OS V1R13, and UA74647 for z/OS V1R12), the System Data Mover (ANTAS000 address space) is changed to conditionally invoke offline device discovery during IPL. Prior to this APAR, offline device discovery was always performed.

APAR OA43706 introduced a new keyword called OfflineDiscovery to the ANTXIN00 parmlib member to allow you to control whether offline device discovery is performed during IPL when ANTAS000 first starts up, and thereafter when ANTAS000 restarts following a CANCEL. A value of YES causes offline discovery to take place. A value of NO bypasses offline device discovery. If OfflineDiscovery is not specified, the default is OfflineDiscovery(NO).

Tip: The Offline Device Discovery was introduced by APAR OA36570 (PTFs for z/OS V1R12 and V1R13) and incorporated into z/OS V2R1 to reduce the XSTART time following an IPL.

SYSLOG messages example:

ANTB8000I XRC INITIALIZATION STARTED 
ANTB8002I OFFLINE DEVICE DISCOVERY COMPLETE; RC=0 REAS=606 
ANTB8001I XRC INITIALIZATION COMPLETED

Element or feature:

DFSMSdfp.

When change was introduced:

z/OS V2R1, z/OS V1R13, and z/OS V1R12, all with APAR OA43706 applied.

Applies to migration from:

z/OS V1R13 and z/OS V1R12, both without APAR OA43706 applied.

Timing:

Before the first IPL of z/OS V2R1.

Is the migration action required?

Yes, if you need offline device discovery to be performed during IPL.

Target system hardware requirements:

None.

Target system software requirements:

None.

Other system (coexistence or fallback) requirements:

None.

Restrictions:

None.

System impacts:

None.

Related IBM® Health Checker for z/OS® check:

None.

Steps to take: You should only need to perform offline device discovery during IPL (i.e. specify OfflineDiscovery(YES) in ANTXIN00) by specifying OfflineDiscovery(YES) if you are using one of the following:

GDPS MzGM (aka XRC) in HYPER-PPRC mode (Incremental Resynch)
GDPS MzGM under z/OS 2.1 with XRC Offline Primary devices

Other XRC configurations or non-XRC environments will not directly benefit from having offline discovery performed at IPL. Therefore, if it is not required, do not specify the keyword and avoid discovery, which may reduce overall IPL elapsed time.

Tip: The value of OfflineDiscovery takes effect when the ANTAS000 address space is started during IPL, or with the automatic restart of ANTAS000 after it has been cancelled. To activate a new value for OfflineDiscovery without an IPL, do the following:

Update the value in PARMLIB member ANTXIN00
Issue the system command CANCEL ANTAS000

The OfflineDiscovery keyword is ignored and will not be processed if it is specified in the ALL or session member of hlq.XCOPY.PARMLIB.

Reference information: z/OS DFSMS Advanced Copy Services