When a system logger application writes a log block to a coupling facility log stream, system logger writes it first to a coupling facility list structure. System logger requires that a coupling facility list structure be associated with each log stream. When the coupling facility structure space allocated for the log stream reaches the installation-defined threshold, system logger moves (offloads) the log blocks from the coupling facility structure to VSAM linear DASD data sets, so that the coupling facility space for the log stream can be used to hold new log blocks. From a user's point of view, the actual location of the log data in the log stream is transparent.