It is possible within Virtual Center using DRS to ensure virtual machines are always on seperate physical hosts. It is also possible to make virtual machines stay together on the same physical server if you needed that.

You might want to do this if you have a microsoft cluster in virtual machines and want to ensure that both cluster node VMs are always on different physical servers. In the meantime you can also benefit from vmotion using DRS of these virtual machines to other physical ESX servers, provided that they are seperate.

1. Right click on the DRS cluster that contains the VMs you want to keep together or seperate.

2. Choose "Edit Settings.

3. Under "VMware DRS" click on "Rules".

4. If any rules already exist you will see them here. To create a rule click "Add".

5. A dialog box will then be displayed. Enter a name for the rule.

5. Choose the type of rule "Seperate virtual machines/Keep virtual machines together".

6. Click "Add" to select the virtual machines the rule applies, then click ok then ok again.

7. You will now see your new rule. Click ok to save and exit the settings.