When MVS™ detects a loss of
connectivity, MVS determines
the viability of rebuilding each structure affected by the connectivity
loss.
If the determination is to initiate a structure rebuild, MVS defers that action until one
of the following occurs:
- The percentage of lost connectivity reaches 100%.
- The internal time value used by MVS expires.
The decision to initiate a structure rebuild is affected by the
sysplex configuration (for example, an environment that is not failure-independent
is recognized) and whether there is an active SFM policy in the sysplex.
- Non Failure-Independent Sysplex Environment
A configuration
that is not vulnerable to a single point of failure is failure-independent.
Having a coupling facility reside on the same physical system as sysplex
members that access it is not a failure-independent configuration.
To handle loss of connectivity in situations where one or more systems
in the sysplex reside on the same physical system as the coupling
facility, systems with OW33615 installed or which are at OS/390® Release 9 or higher provide support
to ensure that structure rebuild is initiated in a timely manner.
Whether
there is an active SFM policy or not, the system declares a loss of
connectivity of 100% when:
- All sysplex members that are failure independent report a loss
of connectivity, and
- Sysplex member(s) that are not failure independent do not report
a similar loss of connectivity.
The assumption is that all members in the same physical
system as the coupling facility have lost connectivity when all other
members have also lost connectivity. Setting the loss of connectivity
percentage to 100% ensures that MVS will
attempt a rebuild of the structures to which connectivity has been
lost in a timely manner.
- Failure-Independent Sysplex Environment
In a
failure-independent sysplex environment, processing is dependent
on whether there is an active SFM policy.
- If MVS determines that there
is an active SFM policy in the sysplex:
- MVS verifies that the SFM
policy data is at the same level on all systems.
- MVS checks the active CFRM
policy to see if a rebuild percent value has been specified for affected
structures, or takes the default rebuild percent value of 1.
- MVS calculates the percentage
of lost connectivity using the system weights specified in the active
SFM policy:
- A = the total value of systems on which there exists a user of
a coupling facility structure that resides in the coupling facility
to which connectivity has been lost.
- B = the total value of systems that have lost connectivity to
the coupling facility and on which there exists a user of a structure
in that coupling facility.
Note that if there are multiple users of a coupling facility
structure on one MVS system,
that system weight is added to each total only once.
- MVS calculates the total
system weight of (A) all systems containing at least one active connection
to the structure in the coupling facility that have lost connectivity,
and (B) all systems containing at least one active connection to a
structure in the coupling facility for which lost connectivity has
been recognized. Note that if there are multiple users of a structure
on one system, that system weight is counted only once.
For example,
if a structure has one connection per system and all systems are of
equal weight 10, then in an eight-system sysplex if one system lost
connectivity, the value of A (total system weight of all systems containing
an active connection that have lost connectivity) is 10 and the value
of B (total system weight of all systems containing an active connection)
is 80.
- MVS determines what action
is to be taken and informs connected users through event exit processing.
The determination is arrived at by dividing A by B, multiplying
by 100, and then comparing the result with the rebuild percent value
for the structure in the active CFRM policy.
- If the result is greater than or equal to REBUILDPERCENT, then MVS initiates a structure rebuild.
- If the result is less than REBUILDPERCENT, MVS does not initiate a rebuild.
In the example above, (10/80)*100 would be the value
compared to the REBUILDPERCENT value. If the value of REBUILDPERCENT
was 13 or higher, a rebuild would not be initiated.
- If MVS determines that there
is not an active SFM policy in the sysplex:
- MVS verifies that rebuild
is supported for the structure.
- MVS initiates the structure
rebuild for any loss of connectivity affecting the structure, regardless
of the REBUILDPERCENT specification, if structure rebuild is supported.
If the determination was to initiate a structure rebuild, MVS defers that action until one
of the following occurs:
- The percentage of lost connectivity reaches 100%.
- The internal time value used by MVS expires.
z/OS MVS Programming: Sysplex Services Guide
Copyright IBM Corporation 1990, 2014