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Enthusiast
Enthusiast

Host isolation response in a 2-node cluster

Hi everyone, I have the following doubt. In a 2-node cluster:

if every node is completely isolated (between them and between witness): (i) if the HA parameter "host isolation response" is set to "power off" then every host power off theire vm; (ii) if is set to "leave powered on" so the vm still powered on. Is that correct?  

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Hot Shot
Hot Shot

Hi Luca. I believe this article would be helpful https://kb.vmware.com/s/article/1030320.

Leave powered on – When a network isolation occurs on the host, the state of the virtual machines remain unchanged and the virtual machines on the isolated host continue to run even if the host can no longer communicate with other hosts in the cluster. This setting also reduces the chances of a false positive. A false positive in this case is an isolated heartbeat network, but a non-isolated virtual machine network and a non-isolated iSCSI/NFS network. Should the host become unresponsive or fail and can no longer access/run the virtual machines, the virtual machines will be registered and powered on by another running host in the cluster. By default, the isolated host leaves its virtual machines powered on.

 

Hope it helps!

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Contributor
Contributor

Hi, 

In general yes, but you must understand that vmdks will be locked/detached from VMs (there will be no writes to disk from Guest OS prospective) no matter you set in HA Isolation Response. vSAN is strong consistency storage, so in case one component lost access to the second copy/component AND witness it will be locked for avoiding split-brain scenario on storage level.

More examples of failures in 2-node scenarios are there - https://core.vmware.com/resource/vsan-2-node-guide#sec11-sub5

 

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Enthusiast
Enthusiast

Ok I read the article. So just to confirm if I well understood: no matter if host isolation response is set to power off or leave powered on: if the cluster is offline (everything is isolated) the vm are powered off on both sites and no one will power on any vm.

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Hot Shot
Hot Shot

This should make things more clear: https://core.vmware.com/resource/vsan-2-node-guide#section11.

 

If the 2 hosts and witness are isolated but powered on, objects will become unavailable since they will lose quorum. Duncan epping explains this in his article: http://www.yellow-bricks.com/2017/11/22/isolation-address-2-node-direct-connect-vsan-environment/

vSAN will now automatically kill all VMs which have lost access to its components

  • The isolated host will lose quorum
  • vSAN objects will become isolated
  • The advanced setting “VSAN.AutoTerminateGhostVm=1” allows vSAN to kill the “ghosted” VMs (with all components inaccessible).