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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.
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