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I recently had to setup anti affinity to separate two guest operating systems that were clustered using Microsoft Cluster. This ensured that each guest would not be on the same host, reducing the risk of hardware failure bringing down both hosts and the cluster. Other examples might be that you want your primary and secondary DNS servers on separate physical hosts, if one host physically dies; you have the other DNS server serving requests.

There are also rules for storage anti affinity (SDRS), it is one thing separating the processing power between different hosts but if both guests are residing on the same storage you are still left with a single point of failure.

I have seen it a few times where there is data replication setup between who virtual guests, DRDB comes to mind, this is great but if the data is stored on the same datastore and that datastore goes down, you have lost both your primary and secondary data.

I will go over how to setup storage anti affinity in a different blog

  1. Right click on your cluster and click on “Edit Settings”
  2. Turn on vSphere DRS if not alreadyTurn on DRS in Cluster
  3. Click on “Rules”
  4. Click “Add”
  5. Type the name you wish to call the rule
  6. Change the type to “Seperate Virtual Machines” Setting up Rule
  7. Click “Add”
  8. Select the servers you wish to seperateSelecting Servers
  9. Click “OK”Finishing Rule Setup
  10. Click “OK”
  11. Expand “+” next to the rule to ensure you have the correct serversCreated Rule
  12. Click “OK”
  13. Ensure “Reconfigure cluster” tasks finishes with “Completed” statusReconfiguring Cluster

There you have it, anti affinity rules setup between two servers.

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