You can configure the coupling facilities both in the processor where z/OS® images run and in a special coupling-facility processor like the IBM 9674 S/390® coupling facility. The former is called an Internal coupling facility, and the latter is called a standalone coupling facility. A

Both z/OS images and a coupling facility could fail at the same time in the event of a processor complex failure. In this situation, some structures cannot be rebuilt in another coupling facility. In general, an internal coupling facility should be used as backup for a production coupling facility if you do not also use coupling-facility duplexing.

A typical standalone coupling facility is an IBM 9674 S/390 coupling facility. If an IBM 9672 in which CFCC runs does not also have a z/OS image from the same Parallel Sysplex®, this internal coupling facility has the same availability as a standalone coupling facility, which gives you the highest availability. At least one of the configured coupling facilities should be standalone.

If you use DFSMStvs under one z/OS system or in a one-processor environment, one internal coupling facility is sufficient. But, if you have a multiple-processor environment, two standalone coupling facilities are recommended for maximum availability. At a minimum, you should have at least one internal coupling facility and one standalone coupling facility.