If you have a DRS enabled cluster in Virtual Infrastructure you might not want certain virtual machines to ever run on the same ESX host.  They might have certain disk I/O or network behaviors you want separated, or it might just be a case of uptime robustness you want like in the case of multiple web servers.

Here is how you can ensure selected virtual machines will never run on the same host-

  1. Right-click on your cluster in VI client, select Edit Settings…
  2. In the wizard, on the left select Rules
  3. On the right, click Add…
  4. Provide a name (like www-separate)
  5. For Type select Separate Virtual Machines
  6. Click Add…
  7. Check off the VMs you want to stay separated.

Ta-da!