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I selected “failover host” and my VMs still end up on a different host after an HA event

Duncan Epping · Mar 2, 2012 ·

I received a question today about HA admission control policies, and more specifically about the “failover host” admission control policy. The question was why VMs were restarted on a different host then selected with the “Failover Host” admission control policy. Shouldn’t this policy guarantee that a VM is restarted on the designated host?

The answer is fairly straight forward, and I thought I blogged about this already but I cannot find it so here it goes. Yes, in a normal condition HA will request the designated failover host to restart the failed VMs. However there are a couple of cases where HA will not restart a VM on the designated failover host(s):

  • When the failover host is not compatible with the virtual machine (portgroup or datastore missing)
  • When the failover host does not have sufficient resource available for the restart
  • When the virtual machine restart fails HA retries on a different host

Keep that in mind when using this admission control policy, it is no hard guarantee that the designated failover host will restart all failed VMs.

Related

BC-DR, Server 4.1, 5.0, admission control, ha, vSphere

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Comments

  1. Salah says

    2 March, 2012 at 14:56

    When VCenter is unavailable admission control policy is unavailable too and the VM get restarted on a different host.

  2. Duncan Epping says

    2 March, 2012 at 15:23

    That has got nothing to do with it… With or without vCenter the HA restart happens on a host layer and is not coordinated by vCenter at all at that point. There is a placement engine which handles this.

  3. Mario says

    2 March, 2012 at 16:55

    Whats about DRS affinity rules? Will the failover host “beats” the DRS rules or is it the other way around?

  4. Duncan Epping says

    2 March, 2012 at 18:28

    HA will not violate “must” rules but will violate “should” rules.

  5. Chris Wahl says

    2 March, 2012 at 23:35

    That’s interesting to know … do you find that “failover host” for HA is all that common? I admit that I have not seen it in a production environment.

  6. Duncan Epping says

    3 March, 2012 at 00:42

    Not common at all Chris. I hardly no any customer using it.

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About the author

Duncan Epping is a Chief Technologist in the Office of CTO of the Cloud Platform BU at VMware. He is a VCDX (# 007), the author of the "vSAN Deep Dive", the “vSphere Clustering Technical Deep Dive” series, and the host of the "Unexplored Territory" podcast.

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