Migrate a VMware Cluster from ESX to ESXi

If you are running ESX, the countdown has begun.  VMware announced in 2010 that after the current release, VSphere 4.1 and the subsequent patches, VMware will no longer be releasing VSphere in the ESX hypervisor architecture flavor.  Due to a general lack of understanding of the differences between the two architectures, many of you may have heard while planning your installation (as did I) that ESX is “better” in some way than ESXi.  This isn’t true, but that is another topic.  More to the point, there are a lot of ESX Cluster installations out there that will at some time have to become ESXi Clusters.

Most admins who use VMware also use HA.  After all, that flexibility and robustness is one of the primary reasons to virtualize, right?  Well, that is where the problem arises.  You see, HA will not allow an “unlike” Host to be added to the cluster.  If the network configuration is not identical, then the host simply cannot be added.  The simple solution is to disable HA.  However, now you can no longer vmotion your virtual machines between hosts.  And at some point, all of those hosts will have to be turned off in order for ESXi to be installed.  Are you seeing the problem here?  So, is there no way to do an in-place cluster upgrade from VMware ESX to VMware ESXi without vm downtime?  Turns out there is!

And it happens to be very simple.  If you too want to rebuild the plane while in flight, first you will need to place the first host in Maintenance Mode, power it off, and install ESXi from the media you downloaded from VMware or the hardware mfg.  Then, add the host back into your datacenter and follow these 6 steps so that you can again add it to the cluster:

  1. Right-click your cluster and select “Edit Settings”. 

    Right-click the cluster and select "Edit"

  2. Verify that the “Host Isolation response” for the cluster is set to “Leave powered on” and that all VMs use the cluster setting. 

    Verify the cluster "Host Isolation" setting

  3. Uncheck “Turn On VMware HA”, click OK, and wait for the task to complete on all hosts in the cluster.

    Uncheck "Turn On VMware HA"

  4. Edit the cluster again.  This time re-check “Turn On VMware HA”, but don’t click OK yet…

    Turn HA back on, but don’t click OK yet…
  5.  First, click on the “Advanced Options” button

    Select "Advanced Options"

  6. Add the following new option: das.bypassNetCompatCheck with a value of True, and then click OK to dismiss all dialog boxes and apply changes.  Then wait once again for the task to complete on all hosts.

    Option: das.bypassNetCompatCheck Value: True

Once all hosts have finished enabling HA, you can drag your upgraded ESXi host back into the cluster.  Don’t forget to disable this advanced option once you have completed migrating the entire cluster to ESXi.  After all, the network compatibility check is there for a reason and is generally a good thing.  Just not in this case!

For more information, see VMware KB article: 1019200

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~ by Jay P Morgan on January 26, 2011.

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