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16 allows one of these protocol exchanges to complete
asynchronously. This allows faster duplexed request ser-
vice time, with more benefi ts when the Coupling Facilities
are further apart, such as in a multi-site Parallel Sysplex
environment.
List notifi cation improvements: Prior to CFCC Level 16,
when a shared queue (subsidiary list) changed state from
empty to non-empty, the CF would notify ALL active con-
nectors. The fi rst one to respond would process the new
message, but when the others tried to do the same, they
would fi nd nothing, incurring additional overhead.
CFCC Level 16 can help improve the effi ciency of coupling
communications for IMS Shared Queue and WebSphere
MQ Shared Queue environments. The Coupling Facility
notifi es only one connector in a sequential fashion. If the
shared queue is processed within a fi xed period of time,
the other connectors do not need to be notifi ed, saving the
cost of the false scheduling. If a shared queue is not read
within the time limit, then the other connectors are notifi ed
as they were prior to CFCC Level 16.
When migrating CF levels, lock, list and cache structure
sizes might need to be increased to support new function.
For example, when you upgrade from CFCC Level 15 to
Level 16 the required size of the structure might increase.
This adjustment can have an impact when the system
allocates structures or copies structures from one coupling
facility to another at different CF levels.
The coupling facility structure sizer tool can size struc-
tures for you and takes into account the amount of space
needed for the current CFCC levels.
Access the tool at:
http://www.ibm.com/servers/eserver/zseries/cfsizer/.
CFCC Level 16 is exclusive to System z10 and is sup-
ported by z/OS and z/VM for guest exploitation.
Coupling Facility Confi guration Alternatives
IBM offers multiple options for confi guring a functioning
Coupling Facility:
• Standalone Coupling Facility: The standalone CF
provides the most “robust” CF capability, as the CPC is
wholly dedicated to running the CFCC microcode — all
of the processors, links and memory are for CF use
only. A natural benefi t of this characteristic is that the
standalone CF is always failure-isolated from exploiting
z/OS software and the server that z/OS is running on for
environments without System-Managed CF Structure
Duplexing. The z10 BC with capacity indicator A00 is
used for systems with ICF(s) only. There are no software
charges associated with such a confi guration.
• Internal Coupling Facility (ICF): Customers consider-
ing clustering technology can get started with Parallel
Sysplex technology at a lower cost by using an ICF
instead of purchasing a standalone Coupling Facility.
An ICF feature is a processor that can only run Coupling
Facility Control Code (CFCC) in a partition. Since CF
LPARs on ICFs are restricted to running only CFCC,
there are no IBM software charges associated with
ICFs. ICFs are ideal for Intelligent Resource Director and
resource sharing environments as well as for data shar-
ing environments where System-Managed CF Structure
Duplexing is exploited.
System-Managed CF Structure Duplexing
System-Managed Coupling Facility (CF) Structure Duplex-
ing provides a general purpose, hardware-assisted, easy-
to-exploit mechanism for duplexing CF structure data. This
provides a robust recovery mechanism for failures such
as loss of a single structure or CF or loss of connectivity to
a single CF, through rapid failover to the backup instance
of the duplexed structure pair. CFCC Level 16 provides CF
Duplexing enhancements described previously in the sec-
tion titled “Coupling Facility Control Code (CFCC) Level 16”.
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