The system guarantees that the primary and secondary structures get allocated in different coupling facilities from one another and gives strong preference to placing the primary and secondary structures in two different coupling facilities that are failure-isolated with respect to each other. If the secondary structure cannot be allocated in a particular coupling facility, message IXC574I indicates the reason.

The allocation algorithm for the secondary structure takes the following considerations into account:

• ENFORCEORDER

  When the installation has specified in the CFRM policy that the preference list order is to be strictly enforced for the structure, the system will only apply those eligibility list considerations (listed below) that involve dropping ineligible coupling facilities from the preference list. MVS™ will not apply any of the considerations that involve weighting the coupling facilities and reordering the preference list based on these attribute weights (considerations for volatility, failure-isolation from connectors, failure-isolation from primary coupling facility, and exclusion list).

• CF-to-CF Link Connectivity

  At the time of the secondary structure allocation, there must be CF-to-CF link connectivity between the coupling facility in which the primary structure is allocated and any coupling facility in which the secondary structure is to be allocated. Any coupling facility in the preference list that does not have CF-to-CF link connectivity to the coupling facility where the primary structure resides is dropped from the eligibility list.

• LOCATION(OTHER)

  The secondary structure cannot be allocated in the same coupling facility as the primary structure under any conditions. The coupling facility that contains the primary structure is dropped from the eligibility list.

• LESSCONNACTION(TERMINATE)

  All active connectors to the primary structure must also have connectivity to the coupling facility in which the secondary structure is to be allocated. Therefore, any coupling facility that does not provide connectivity for all current active connectors to the structure is dropped from the eligibility list.

  When there are no active connectors to the structure, MVS may allow the allocation of the secondary structure in a coupling facility that has less connectivity to systems than does the coupling facility in which the primary structure is allocated. If, at a later time, a connector attempts to connect to the now-duplexed structure and MVS observes that the connector is running on a system that does not have connectivity to both structure instances, MVS will drop the structure out of duplexing. The structure instance that will be kept is that which is accessible to the connector. Note that after the connector connects, MVS may subsequently reduplex the structure into another coupling facility that does provide full connectivity for the set of active connectors to the structure.

• POPULATECF

  The concept of “POPULATECF” is not applicable to a duplexing rebuild, and thus does not affect the allocation of a secondary structure. Rebuild processes of any kind cannot be initiated against a duplexed structure.

• Available Space
  In order to create a secondary structure that is an exact copy of the primary structure (exact structure attributes and same total and maximum structure counts for all structure objects), it might be necessary for MVS to allocate the secondary structure with a size that significantly differs from that of the primary structure. This is because of different coupling facility storage allocation mechanisms that may exist at different CFLEVELs. Therefore, MVS will process each coupling facility in the preference list as follows:

  • Determine the target size (and minimum required control space) of a structure allocated in this particular coupling facility that has the same structure attributes and total and maximum object counts as the primary structure. Note that the maximum structure size from the CFRM policy is not used as an upper bound to the determined target structure; rather, the maximum structure size is allowed to “float” to whatever size is necessary to accomodate the number of structure objects that exist in the primary structure.
  • Compare the determined target size and minimum required control space results to the actual free space and free control space in this coupling facility.
    • If the coupling facility has sufficient free space and free control space to accomodate the allocation of the structure, include this coupling facility in the eligibility list.
    • If not, drop this coupling facility from the eligibility list.
• CFLEVEL

  System-managed duplexing rebuild requires a coupling facility of CFLEVEL=11 or higher, so any coupling facility in the preference list which is at a lower CFLEVEL is dropped from the eligibility list.

• Volatility

  If any active or failed-persistent connectors to the structure requested non-volatility, the system will give preference in the eligibility list to allocating the structure in a nonvolatile coupling facility, using the normal eligibility list weighting for non-volatility.

• Failure-isolation from Connectors

  If any active or failed-persistent connectors to the structure requested non-volatility (and thus implicitly requested failure-isolation), MVS will give preference to allocating the secondary structure in a coupling facility that is standalone, that is, failure-isolated with respect to all active connectors to the structure.

  Non-standalone coupling facilities, which do not provide failure-isolation from all active connectors, will be allowed to remain in the eligibility list, but behind those that do provide full failure-isolation, using the normal eligibility list weighting for failure-isolation.

• Failure-isolation from Primary Coupling Facility

  MVS will give preference to allocating the secondary structure in a coupling facility that is duplex failure-isolated (that is, in a different processor) from the coupling facility in which the primary structure is allocated. Coupling facilities that do not provide failure-isolation from the primary coupling facility will be allowed to remain in the eligibility list, behind all coupling facilities that do provide this failure-isolation. This failure-isolation from the primary coupling facility is a very high-weighted attribute in determining the eligibility list order.

  If the secondary structure is allocated in a coupling facility that is not duplex failure-isolated from the primary, MVS issues a highlighted eventual action warning message, IXC553E, to warn about the lack of CF-to-CF failure-isolation.

• Exclusion List

  The system prefers to allocate the secondary structure in a coupling facility that does not contain any allocated structure instances (primary or secondary) for any structure listed in this structure's exclusion list. However, there may be instances when a structure is listed in an exclusion list and has already been duplexed. In that case, the following exclusion list processing occurs:

  1. The system chooses to allocate the secondary structure in a coupling facility where neither instance of the structure listed in the exclusion list resides.
  2. The system chooses to allocate the secondary structure in a coupling facility where one instance of the structure listed in the exclusion list resides, but there is another instance of the duplexed structure in a coupling facility separate from the coupling facility containing the structure awaiting to be duplexed.
  3. The system chooses to allocate the secondary structure in a coupling facility where one instance of the structure listed in the exclusion list resides, and the other instance of the duplexed pair does not reside in a separate coupling facility.

  Both options 2 and 3 are not considered to have met the exclusion list requirement and therefore the system will set CONAIGNOREDEXCLUSIONLIST ON.

• Application of Pending Policy

  The system will not initiate system-managed duplexing rebuild processing while a CFRM policy change is pending against a structure or when, during the process of allocating a duplexed structure, the system discovers that a policy change is pending. When such a policy change is pending, the installation must take whatever action against the structure is required to cause the pending policy change to take effect. This generally involves rebuilding the structure through either a user-managed or system-managed rebuild process, or causing the structure to be deallocated or reallocated.

• Model-dependent Limit on Number of Connectors

  It is necessary that all connectors to the primary (or old) structure can be attached to the secondary (or new) structure with the same Connection ID number. The maximum number of connectors to a structure of a given type is a model-dependent coupling facility attribute, and therefore it is possible that some of the coupling facilities in the preference list have a limit that is too low to accommodate all of the attachments that are present in the old structure at this time. Any coupling facility whose model-dependent limit on the number of connectors is insufficient will be dropped from the eligibility list.