The difference between Quorum and fencing

[djahida]

Hello,

Can you please explain me the difference between quorum and fencing ?
Can I configure a cluster Proxmox V3.4 with 2 nodes (HA) and VM Quorum without Fencing?
To explain my configuration

• I have configure cluster proxmox with 2 nodes + one quorum
• When i try to simulate a fail network with service networking stop, just to verfy if my VM will migrate to the other node. I have this error: fence xxxxxx dev 0.0 agent none result: error no method
• I just activate the fencing in the /etc/default/redhat-cluster-pve

In the case of, the fencing must be configured to ensure the HA, can I used the same network interface for fencing and to access to the node?

Thanks for your help

 

[m.ardito]

afaik, in simple words:

quorum is a rule to guarantee a coherent cluster status by multiple nodes (ie: majority of nodes see the same resources and can communicate properly)

fencing is an isolation method for isolate failing cluster nodes to prevent problems when/if they come back (ie: if a vm of a failed node was restarted elsewhere, if that node comes up and is not isolated, there could be conflicts for the VM and/or else)
fencing also needs proper hardware fencing devices and a good setup.

without quorum, a cluster (with/without HA) is in a dangerous state and cannot work properly. if there is a quorum, cluster operations are (relatively) safe. proper HA setups, using fencing, can ensure that the cluster, when it has quorum, is really safe (since failed nodes are isolated and cannot restart automatically) so that vm on failed nodes can be safely restarted (from backups) on other nodes in the cluster.

Marco

 

[djahida]

Thanks Marco
Its more clear for me
But i stil dont know how can I configure fencing
I think that i have to configure it on the network device, can I use the same interface?

 

[m.ardito]

Thanks Marco
Its more clear for me
But i stil dont know how can I configure fencing
I think that i have to configure it on the network device, can I use the same interface?

fencing is a complex topic, but you should refer to, at least:

http://pve.proxmox.com/wiki/High_Availability_Cluster
http://pve.proxmox.com/wiki/Fencing

I only have used a simple non HA cluster...

Marco

 

[KnowVation]

Hi!

For a quorum, you need at least three nodes. If you have only two, simulate the third with the "quorum disk".

Fencing is the most important thing for realizing the HighAvailability with proxmox.

Roman

 

[djahida]

Thank you Marco

 

[djahida]

For the Quorum, I used a virtual machine
Now, I try to configure fencing

Thanks for the reply Roman

 

[KnowVation]

No Problem djahida!

Ok, that should be not a problem with a virtual machine.
Which kind of fencing device will you choose?
Fencing via PDUs, Switch, UPSs,..

Roman

 

[djahida]

I have two DELL server Power edge, with iDRAC devices
So I am trying to configure it
Do you have any idea, if this solution can guarantee an HA for the cluster?

Djahida

 

[KnowVation]

When you use this https://pve.proxmox.com/wiki/Two-Node_High_Availability_Cluster for den Quorum configuration, the HA should work.

Roman