On 26/04/16 08:15 AM, RaSca wrote: > Il 26/04/2016 13:39, K Aravind ha scritto: >> Hi all >> Have some doubts regarding pacemaker >> It would be of great help if you could help me out >> >> 1.Pacemaker handles split brains using quorum and stonith only right .? >> It is not a case where a split brain is resolved wothout the use of >> stonith and qourm am I right ? > > Not by default. But if you set no-quorum-policy according to what you > want to achieve you may obtain something similar to a split brain > resolution.
Note that quorum has nothing to do with split-brain protection, only stonith does. Quorum is used to prevent a sole node (that is operating properly, say after a reboot) from trying to run cluster services when it is inquorate. Said another way; Stonith/Fencing is a tool to protect your cluster when things go wrong. Quorum is a tool to help your nodes make decisions when things are working properly. >> 2.Resource stickiness /location cannot be used to solve split brain right ? > > Again, it depends. For example if you set a location based upon the > network connectivity, then you may obtain that a disconnected node will > not run any resource. > That said if you want to be 100% sure you must use stonith. > >> 3.let's say I have qourum enabled but not stonith for a two node cluster >> ..can it be used for solving split brain ..if so can the user >> application can add rules for quorum to elect appropriate / preffered >> the master ..similar to resource stickiness ? > > Again, see no-quorum-policy. To again clarify; No. Quorum does not help prevent split-brains and quorum can not be used on 2-node clusters at any rate. Quorum only works on 3+ node clusters because quorum is calculated as: 50% of total votes, plus 1, rounded down. 2 Node == 2 / 1 = 1 + 1 = 2 rounded down to 2. 3 Nodes == 3 / 2 = 1.5 + 1 = 2.5 rounded down to 2. 4 Nodes == 4 / 2 = 2 + 1 = 3 rounded down to 3. 5 Nodes == 5 / 2 = 2.5 + 1 = 3.5 rounded down to 3. So, quorum in a 2-node cluster is '2', meaning the cluster will shut down if one node fails. Not very HA :). 3 and 4 node clusters can each lose 1 node, 5 nodes can lose 2 nodes, and so on. >> 4.can I configure the default role for a node ? >> Meaning ...let's say I have a two node master slave setup >> ,master node goes down and the slave is elected as a master so far so >> good now let's say the older master which was down comes up. So is there >> a way I can configure it be slave by default meaning whenever a new node >> comes up it be a slave and not a master > > You can work on default resource stickiness to INFINITY in this case. > >> 5.Can I have node roles other than master or slave in a master slave >> cluster say unknown ? > > No, AFAIK. > >> 6.Is there notification from pacemaker when a split brain happens , >> When an election beings , >> When an election is done >> Thanks >> Aravind > > Just in the logs, but you can setup something like email notification > for each action. I don't know how things are now, but in the past those > were a lot of mail (and when I say a lot I mean a LOT). > > Bye, With stonith enabled, a failed fence will leave the cluster hung, by design. The logic is that, as bad as a hung cluster is, it is better than risking a split-brain (which can lead to data loss / corruption, confused switches, etc). digimer -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education? _______________________________________________ Users mailing list: [email protected] http://clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org
