The invention is an improvement to a storage virtualization system that enables the system to determine a class of service for potential storage devices and allows a user, administrator, or application to select a minimum class of service for any given type of data. The class of service is based upon factors that reflect a potential storage device's reliability, such as the device type and historical uptime data. In a P2P environment, the class of service also includes additional factors, such as the type of attached processing unit and the type of operating system running the attached processing unit.