The process of allocating the new structure differs significantly between system-managed rebuild and duplexing rebuild, primarily because of the stringent coupling facility requirements needed by duplexing rebuild.

• System-managed Rebuild
  The system determines the location of the new structure using the following guidelines:

  • If the request to start the rebuild specified POPULATECF, only the specified coupling facility is a valid rebuild target.
  • If the request to start the rebuild specified LOCATION=OTHER or there is no pending policy change affecting the relevant structure, the new structure will not be allocated in the same coupling facility as the original structure.
  • The new structure will not be allocated in the same coupling facility as the original structure unless one of the following is true:
    • There is a pending policy change that does not involve a change to the structure SIZE or INITSIZE.
    • There is a pending policy change that affects SIZE or INITSIZE, and all active or failed-persistent connectors specified IXLCONN ALLOWALTER=YES.
  • The allocating system allocates the structure in the first coupling facility in the preference list that meets the standard allocation requirements, with the following additional requirements.
    • The coupling facility must have sufficient available storage to allocate a new structure that will be large enough to contain all the data to be copied from the old structure.
    • The coupling facility must be at a CFLEVEL sufficient to support the system-managed rebuild process. System-managed rebuild requires a coupling facility of CFLEVEL=8 or higher.
    • The CFLEVEL must be as least as high as the CFLEVEL reported to connectors when they connected to the original structure.
    • All systems in the sysplex with active connectors to the structure undergoing system-managed rebuild must have connectivity to the coupling facility.

  The system stops the rebuild process if there is no coupling facility that meets the allocation requirements.

  Connectors do not have the option of changing structure attributes during a system-managed rebuild. In the new structure, the attributes that can be specified on IXLCONN will be identical to those of the old structure, with the following possible exceptions:

  • If there is a pending CFRM policy change that modifies the structure SIZE or INITSIZE, and all active and failed-persistent connectors specified IXLCONN ALLOWALTER=YES, the system will allocate the new structure using the sizes from the pending policy, subject to the requirement that the resulting size must be large enough to contain the data to be copied from the old structure. In this case, resulting structure attributes such as entry-to-element ratios may differ from the values originally specified by connectors.

    Whether or not structure attributes change during a system-managed rebuild, if all connectors specified IXLCONN ALLOWALTER=YES the system will present Alter Begin and Alter End events to the event exits of active connectors at the conclusion of system-managed rebuild processing (after the Structure Available event has been delivered).

  • For list and lock structures, if the coupling facility model-dependent limit for the maximum number of connectors to a structure of a given type is different for the new structure instance and all the connectors to the old structure instance support user-id limit changes by specifying MAXCONN on the IXLCONN, the resulting structure attribute, user-id limit,for the new structure instance can differ from the value of the old structure instance. XCF communicates the user-id limit change through the structure state change event.
• System-managed Duplexing Rebuild

  The system will always assume a rebuild attribute of LOCATION=OTHER when allocating the secondary structure, so that the primary and secondary instances are allocated in two different coupling facilities. When there are active connectors to the structure, the system will also assume a rebuild attribute of LESSCONNACTION=TERMINATE, so that the attempt to start duplexing for the structure will be automatically stopped if it would cause a loss of coupling facility connectivity for any active connector to the structure. Lastly, the system will give strong preference to placing the structures in two different coupling facilities that are failure-isolated with respect to one another.

  Determining the eligibility of a coupling facility in which to allocate 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 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 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 connectivity to the coupling facility where the primary structure resides is dropped from the eligibility list. Message IXC574I and CONAFACILITYARRAY indicate the reason why the secondary structure could not be allocated in a particular coupling facility.

  • 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.

    In addition, the secondary structure must be allocated in a coupling facility that is at least at a CFLEVEL as high as, or higher than, the highest CFLEVEL that has been reported back to any connector to the structure via IXLYCONA at any time since the primary structure was allocated. This CFLEVEL will be the lower of either (a) the actual CFLEVEL of the coupling facility in which the primary structure is allocated, or (b) the highest requested CFLEVEL value requested by any past or present connector to the primary structure. Any coupling facilities that are not at this minimum required CFLEVEL or higher are dropped from the eligibility list.

  • Volatility

    If any active or failed-persistent connectors to the structure requested nonvolatility, 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 nonvolatility.

  • Failure-isolation from Connectors

    If any active or failed-persistent connectors to the structure requested nonvolatility (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, coupling facilities containing such structure instances will be allowed to remain on the eligibility list, subsequent to those that do not contain such structures, given the normal exclusion list eligibility list weighting.

  • Application of Pending Policy

    The system will not initiate system-managed duplexing rebuild processing while a CFRM policy change is pending against a structure. 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.

  Connectors do not have the option of changing structure attributes during a system-managed duplexing rebuild. In the new structure, the attributes that can be specified on IXLCONN will be identical to those of the old structure, with the following possible exception:

  • For list and lock structures, if the coupling facility model-dependent limit for the maximum number of connectors to a structure of a given type is different for the new structure instance and all the connectors to the old structure instance support user-id limit changes by specifying MAXCONN on the IXLCONN, the resulting structure attribute and user-id limit, for the new structure instance might differ from the value of the old structure instance. XCF communicates the user id-limit change through the structure state change event when the duplexing rebuild process is stopped to switch to the new (secondary) instance.