The PREMODE tells SSM how to perform prereq or subreq processing for the resource that is being processed. Meaning if processing RESA, and its CS=DOWN DS=UP, SSM internally would do prereq checking based on the setting of its PREMODE value. If PREMODE=PREREQ for RESA, then SSM only would check to see if the PREREQs for RESA are UP. With PREMODE=PREREQ for RESA, when you go to shutdown it down (CS=UP DS=DOWN), SSM would not check for subreqs (it would ignore any other resource that has a PREREQ=RESA). So this is one setup that would do what is being asked - Setting PREMODE=PREREQ for ALPHA .
The REFMODE setting tells SSM how to process a resource when it is being REFerred or looked at as a prereq or subreq when SSM is processing some other resource. Meaning, if you attempt to stop RESA (CS=UP/DS=DOWN), SSM would look at or refer to all other SSM resources that have PREREQ=RESA. Then based on the REFMODE of that referred resource (the dependent resources), SSM would check its CS to make sure it is DOWN since you are requesting to stop RESA. But if the REFMODE=PREREQ for the referred (subreq) resource is set, SSM would ignore since REFMODE=PREREQ means only process in a prereq conditions. So another method you could do here to get ALPHA to stop without shutting down ‘subreqs’ is to set these subreqs (BETA,GAMMA) with REFMODE=PREREQ.
The resource MODE controls the overall processing of the resource being processed (should it perform prereq and subreq with MODE=ACTIVE, or not do prereq/subreq checking with MODE=NOPREREQ). Additionally the MODE can be used to tell SSM to not react to ACTION events (UP_DOWN/DOWN_UP,etc) and only monitor or set the resources CS=DS based on CS setting with MODE=PASSIVE.
The technique chosen depends on the overall ‘need’ and if the need changes based on doing things one way at system startup, versus system shutdown, versus a recycle of a resource,etc. If you are simply needing to ‘bounce’ ALPHA then look at another option like that outlined in the FCYCLE subroutine of the hql.CCLXRULS(SSMCNTL) sample. This sample SSM external control rule demonstrates another technique of forcing down a resource and restarting without doing any subreq checking – SSM FCYCLE JOB=ALPA – would bring it down, then restart.