Red Alert : Fix for XES APAR OA37264 needed for z196 GA2 or z114

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Fix for APAR OA37264 needed on z/OS 1.10 and higher for exploitation of greater than 64 subchannels to a Coupling Facility when running on z196 GA2 or z114 at Driver 93G

Abstract:
A dynamic activate to add a coupling facility control unit configured with greater than 64 subchannels using HCD z196 GA2 and z114 support (OA32576) may lead to system or sysplex outage when the z/OS images reside on z196 GA2 or z114.

Description:
z/OS images on a z196 or z114 at Driver 93G connected to a coupling facility on a z196 or z114 at Driver 93G using 3 or more infiniband links that are defined with 32 subchannels per CHPID will exceed 64 subchannels to the CF and may experience the problem described by XES APAR OA37264. The default for IFB links changed from 7 to 32 subchannels per CHPID with HCD APAR OA32576 installed for greater than 7 subchannel support.

When configured as noted above, any dynamic HCD activate which generates a new control unit accessing the coupling facility may lead to the problem. Please see APAR OA37264 which is applicable to z/OS 1.10, 1.11, 1.12 and 1.13 releases for more details.

Recommended Actions:
For installations migrating to z196 GA2 (DR93) level machine or z114, please take one of the following actions:

1. At I/O definition time, do not take the default in HCD of 32 subchannels for IFB links introduced in OA32576. Explicitly specify 7 subchannels per CHPID before proceeding with dynamic activation.
2. Only define and configure online 2 CF links with 32 subchannels for each coupling facility control unit. Note: 32 subchannels per CHPID will be set by default.
3. Apply ++APAR for OA37264 to all z/OS images before exploiting the use of 32 subchannels per CHPID when 3 or more CHPIDs are defined for a CF control unit.

For installations currently configured with greater than 64 subchannels to the CF, please consider all of the following actions:

1. Do not perform a dynamic activate to add a CF control unit to z/OS images to use more than 64 coupling facility subchannels per CF control unit.
2. If a dynamic activate was performed which created a new CF control unit, do not attempt to bring online more than 64 subchannels (2 CHPIDs). Note: If the z/OS image has been IPLd since the dynamic activate was done the system can successfully exploit the greater than 64 subchannel support.
3. Roll ++APAR OA37264 ASAP if greater than 64 subchannel support is needed.

If 64 or fewer coupling facility subchannels are currently defined to each coupling facility control unit, no action is required.

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