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It is frustrating to have your virtualization goals hampered by restrictive licensing policies based on the old physical server paradigm.   Back in the day when a cluster was a pair of identical servers dedicated to hosting a single application a server based license model made sense.  However, when I move these apps into VMs running in a consolidated architecture on large HA/DRS clusters, having to pay to license each physical server not only makes things prohibitively expensive it just doesn’t make sense.

Unfortunately, some software vendors haven’t been very cooperative when it comes to adapting their outdated pricing models for virtual server environments.  As a result some people have been forced to either keep some applications on physical servers or get creative and re-architect their virtual environment to mimic the older physical architecture.  Neither is a good long tem solution.

The good news is with vSphere 4.1 dealing with server based licensing is no longer a problem.  In 4.1 VMware introduced DRS VM-Host Affinity Rules which allow you restrict the ESX hosts on which a VM or group of VMs can run.  To do this you simply define an ESX “Host-Group” together with a virtual machine “VM-Group” and set a rule that the VM(s) in the VM-Group can only run on the ESX hosts in the Host-Group. 

The result is in a large HA/DRS cluster you can now pay to license just two or three of the ESX hosts and then restrict the applicable VMs to only run on one of the licensed servers.

DRS VM-Host Affinity

For more information on DRS VM-Host affinity rules check out this excellent blog by the well-known DRS expert Frank Denneman.  DRS Host Groups are also documented in the Using VM-Host Affinity Rules section of the vSphere 4.1 Resource Management Guide.