2Node Cluster two_node

[bumann]

Hi,

i have read in forum to use two_node="1" expected_votes="1" option for two node cluster config to not went into problem when one node fails. The problem, i cant find the cluster.conf file in Prox VE 4.2. But i found the corosync.conf. Should i insert only

quorum {
provider: corosync_votequorum
two_node: 1
}

into to solve the "one node alive" problem?!

 

[dietmar]

Please do not use those options with Proxmox VE 4.2. It is dangerous and not recommended.

 

[bumann]

can you give me the reason why it is not recommended?
What settings are good to normal use the second node in a two node cluster it the first node crash?

 

[bumann]

?

 

[dietmar]

It is dangerous because it can/will lead to a split-brain situation.

 

[CBdVSdFSMB]

can you give me the reason why it is not recommended?

That's very simple (once somebody explains it): Imagine a situation in which the two nodes lose their communication between each other. Both are alive and able to work alone, but they see that the other node is down (at least from their perspective). Which one of them will take over the whole work (aka host the VMs which ran on the other node until the crash happened)? Who is right and takes them over? Both will try to do so and block or destroy each other as both of them have one vote and the expected quorum is 1 -> both are right/alive/...

When you use at least three nodes and one single node fails, the other two see each other, put their votes together and have a majority (2 out of 3 votes). They can kill the failed node by shutting him down (if that didn't happen in the first place) and continue their work.

Cheers, Johannes