IBM System Management Facility (SMF) is a component of IBM's z/OS for mainframe computers, providing a standardised method for writing out records of activity to a file (or data set to use a z/OS term).
SMF provides full "instrumentation" of all baseline activities running on that IBM mainframe operating system, including I/O, network activity, software usage, error conditions, processor utilization, etc.
One of the most prominent components of z/OS that uses SMF is the IBM Resource Measurement Facility (RMF).
RMF provides performance and usage instrumentation of resources such as processor, memory, disk, cache, workload, virtual storage, XCF and Coupling Facility.
Different processor families and Coupling Facility levels also change the data model.