Am 21.03.2013 um 13:32 schrieb Ron Kerry <[email protected]>: > 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.
It seems you are in the same situation like me (last week) :-) So far i will provide my big picture. Deeper insights must be provided from the experts here. > 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? AFAIK - the architecture should be seen mainly as a stack. On top of all is the so called "cluster resource manager (crm)" like pacemaker or rgmanager. Lets call it crm-layer and we use pacemaker for it (check "pacemaker internals" in the documentation). Under the crm-layer is the communication layer (corosync) that checks e.g. cluster membership. Membership is the keyword here when we take a look at cman - the quorum-concept handles the active cluster/members and this can be also done by pacemaker/corosync. cman can do this (quorum handling) very well (mature code) and is doing this in the lower layers (extending corosync) - so thats the difference. When the lower level has some information (e.g. about the quorum status) then all upper levels have the same information. If pacemaker is doing this then they might be situations where different informations exists in the different levels/layers. > 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? cman is part of the RH cluster suite - the motivations of the different ha approaches for both vendors are for sure more based in strategic/marketing needs. -- LF _______________________________________________ Pacemaker mailing list: [email protected] http://oss.clusterlabs.org/mailman/listinfo/pacemaker Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org
