IBM z/OS - page 33

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.