[Pacemaker] CMAN, corosync & pacemaker

[Ron Kerry]

I believe I understand how to configure CMAN to work with corosync and pacemaker, but I do not 
really understand what roles these three packages all play. Perhaps this information is exposed in 
the written documentation that is available in various places, but I have not been able to discern it.

You can run the corosync/pacemaker (either ver=0 or ver=1) combination and get fully functioning HA 
clusters. What does adding CMAN to the mix add to the functionality? Or perhaps a better question, 
what functions does CMAN take over from either corosync or pacemaker and why is this considered a 
better combination? What are the deficiencies in corosync that running CMAN on top of it resolves?

I believe the preferred pacemaker based HA configuration in RHEL 6.4 uses all three packages and the 
preferred configuration in SLES11 SP2 is just corosync/pacemaker (I do not believe CMAN is even 
available in SLE-HAE). Why the different approaches and what is the advantage of each configuration?

-- 

Ron Kerry