The coupling facility dump space is an area within the coupling facility that you reserve for dumping structure data. Systems in the sysplex can request that an SVC dump be taken to capture structure data. SVC dump serializes each structure to be dumped to keep the structure's control information from changing. SVC dump uses the coupling facility dump space to quickly capture structure control information so that dump serialization is held for as brief a time as possible. The captured control information is written to an SVC dump data set after dump serialization is released. (Note: The maximum amount of time that SVC dump is allowed to hold serialization on the structure is specified initially when the application connects to the structure. The operator can override that amount of time with the DUMP or CHNGDUMP command.)

You can define only one dump space in each coupling facility; however, that dump space can contain several structure dump tables. IBM® recommends that you specify 5% of the available storage in a coupling facility for dump space. If you do not specify any coupling facility dump space, none will be allocated and no structures in the coupling facility can be dumped.

You can determine how the dump space in a coupling facility is being utilized by using RMF™ reports or the DISPLAY CF command. Information returned includes the total amount of storage in the coupling facility, the amount not being used, and information about the dump space.

You might need to change to a larger coupling facility dump space if you find that you are receiving partial SVC dumps because there is not enough available space to hold the structure information. Conversely, you might need to decrease the amount of dump space if you find that the space is not being used or that its size is causing structure allocations to fail or to be allocated in a less preferable coupling facility.

To change the size of the dump space defined in the active CFRM policy, you must redefine the amount of dump space for the coupling facility in a CFRM administrative policy and follow normal procedures for switching from one policy to another, such as with the SETXCF START,POLICY command.