For example, suppose an installation defined three data sets, DS1, DS2, and DS3, in that order on the DSNAME parameter of SMFPRMxx. Now, lets say that SMF is writing to DS2, while DS1 and DS3 are empty. When DS2 fills, the installation issues I SMF to switch to an empty data set, SMF will use data set DS1 because it is at the top of the list in SMFPRMxx.
If the first available data set is not completely empty, SMF will begin to store the records in its buffers, even though there might be enough room in that data set for the records it is trying to write, and even though others of the SMF data sets might be completely empty.
Full means that the record which SMF is currently preparing to write out will not fit into the space left on the current SMF data set. It is possible that a data set might become “full” when it is less than 100% filled.
To prepare an SMF data set for dumping before it becomes full, the operator uses the SWITCH SMF command. When switching the SMF data sets, an inactive data set cannot become active unless it is empty. Therefore, before issuing the SWITCH command, the operator should use the DISPLAY SMF command to verify that there is at least one alternate data set. If the operator does not make this check, data might be lost.
The HALT EOD command causes a switch of SMF data sets but should be used only if the operator intends to quiesce the system in preparation to shut down. The HALT command should never be used if you intend to keep running, because it closes the system log.