Coupling Facility Conﬁguration Alternatives

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 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 availability 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 Conﬁguration Alternatives

IBM offers different options for conﬁ guring a functioning Coupling Facility:

•Standalone Coupling Facility: z900 Model 100 and z800 Model 0CF servers provide a physically isolated, totally independent CF environment. Like the z990, there is no unique standalone coupling facility model offered with the z890. Customers can achieve the same physically isolated environment as on prior mainframe families by ordering a z890 or z990 with PUs characterized as ICFs and general purpose PUs. 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 zSeries 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 processing 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.

•Dynamic ICF Expansion: Dynamic ICF expansion pro- vides value by providing extra CF capacity when there are unexpected peaks in the workload or in case of loss of CF capacity in the cluster.