IBM z/OS - Manual (Page 33)

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Although there is a signifi cant value in a single footprint
and multi-footprint environment with resource sharing,
those customers looking for high availability must move
on to a database data sharing confi guration. With the
Parallel Sysplex environment, combined with the Workload
Manager and CICS TS or IMS TM, incoming work can be
dynamically routed to the z/OS or the OS/390 image most
capable of handling the work. This dynamic workload
balancing, along with the capability to have read/write
access data from anywhere in the Parallel Sysplex cluster,
provides the scalability and availability that businesses
demand today. When confi gured properly, a Parallel
Sysplex cluster has no single point of failure and can
provide customers with near continuous application avail-
ability over planned and unplanned outages. For detailed
information on IBM’s Parallel Sysplex technology, visit our
Parallel Sysplex home page at ibm.com/servers/eserver/
zseries/pso.
Coupling Facility Confi guration Alternatives
IBM offers different options for confi guring a functioning
Coupling Facility:
• Standalone Coupling Facility: z900 Model 100, z800
Model 0CF and 9672-R06 models provide a physically
isolated, totally independent CF environment. There is
no unique standalone coupling facility model offered
with the z990. Customers can achieve the same physi-
cally isolated environment as on prior mainframe families
by ordering a z990 with PUs characterized as ICFs.
There are no software charges associated with such
confi guration. An ICF or CF partition sharing a server
with any operating system images not in the sysplex
acts like a logical standalone CF.
• 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.
• Coupling Facility partition on a z990, z900, z800 or 9672
server using standard LPAR: A CF can be confi gured
to run in either a dedicated or shared CP partition. IBM
software charges apply. This may be a good alternative
for test confi gurations that require very little CF process-
ing resource or for providing hot-standby CF backup
using the Dynamic Coupling Facility Dispatching function.
A Coupling Facility can be confi gured to take advantage of
a combination of different Parallel Sysplex capabilities:
• Dynamic CF Dispatch: Prior to the availability of the
Dynamic CF Dispatch algorithm, shared CF partitions
could only use the “active wait” algorithm. With active
wait, a CF partition uses all of its allotted time-slice,
whether it has any requests to service or not. The
optional Dynamic CF Dispatch algorithm puts a CF parti-
tion to “sleep” when there are no requests to service and
the longer there are no requests, the longer the partition
sleeps. Although less responsive than the active wait
algorithm, Dynamic CF Dispatch will conserve CP or ICF
resources when a CF partition has no work to process
and will make the resources available to other partitions
sharing the resource. Dynamic CF Dispatch can be
used for test CFs and also for creating a hot-standby
partition to back up an active CF.