Your case here would be based on the benefits of virtualisation in general rather than best practices for a file server. File servers do not to tend to be seen as resource intensive and requiring special configuration in a virtual environment as opposed to a physical. You should sell the HA, backup and disaster recovery benefits of virtualisation over physical implementations.
What are the customers stance on physical/virtual and their concerns? what does the file server/s mean to their business i.e. are they critical? why are they reluctant to virtualise?
