by steve-myers » Thu Aug 02, 2012 9:16 am
In my experience, z/OS systems tend to be unusable long before they are actually shut down, even when unusable, some subsystems may be active and at least partially usable even when the system as a whole is unusable. You can usually directly retrieve from SMF data when individual subsystems are taken down during a system shut down. Of course, if the system died when the power grid died, no system data may be recorded.
Similarly, IPL time does not reveal when the major subsystems become active; this may not happen for some time after an IPL. Many subsystems require the network to be running before they can be considered usable.