A coupling facility becomes volatile

If a coupling facility changes to the volatile state, the system logger on each system using the coupling facility structure is notified. For structures that are in simplex-mode, a dynamic rebuild of the structure is initiated so that the log data can be moved to a non-volatile coupling facility. During rebuild processing, system logger rejects any logger service requests. If there is not a structure available in a non-volatile coupling facility, system logger will still rebuild the data on a new volatile coupling facility.

System logger may then change the way it duplexes coupling facility data because the volatile coupling facility constitutes a single point of failure:

For log streams defined with STG_DUPLEX=YES, system logger will begin duplexing data to staging data sets, if they were not already in use.
For log streams defined with STG_DUPLEX=NO, system logger will keep on duplexing data to local storage buffers on each system.

For duplex-mode structures, dynamic structure rebuild is not supported because there are already two copies of the structure. However, system logger may change whether it will duplex the log data and the way it duplexes the data since the new composite coupling facility volatility state constitutes a single point of failure.

Assume the initial environment had a non-volatile composite structure coupling facility state but there was a failure-dependent relationship between the connecting system and the composite structure view.
The log stream was considered to be in a single point of failure environment and still is after the state change, so logger makes no changes to the duplexed method.
Assume the initial environment had a non-volatile composite structure coupling facility state and there was a failure-independent connection between the connecting system and the composite structure view, but there was a failure-dependent relationship between the two structure instances.
The log stream was not considered to be in a single point of failure environment, but would be after the coupling facility state changed to volatile. Logger would continue to duplex the log data, but might change the duplexing method.
- For log streams defined with STG_DUPLEX=YES, system logger will begin duplexing data to staging data sets, if they were not already in use.
Assume the initial environment had a non-volatile composite structure coupling facility state, there was a failure-independent connection between the connecting system and the composite structure view, and there was a failure-independent relationship between the two structure instances.
The log stream was not considered to be in a single point of failure environment, but would be after the coupling facility state changed to volatile.
- For log streams defined with LOGGERDUPLEX(UNCOND), system logger will continue to duplex the log data. However, for log streams defined with STG_DUPLEX=YES, system logger will begin duplexing data to staging data sets, if they were not already in use.
- For log streams defined with LOGGERDUPLEX(COND), system logger will first offload the log data from the structure, then begin duplexing any new log data written to the log stream.
  - For log streams defined with STG_DUPLEX=NO, logger will begin duplexing data to local buffers.
  - For log streams defined with STG_DUPLEX=YES, logger will begin duplexing data to staging data sets.