The design and operation of very large-scale storage systems is an area ripe for application of automated design and management techniques - and at the heart of such techniques is the need to represent storage system QoS in many guises: the goals (service level requirements) for the storage system, predictions for the design that results, enforcement constraints for the runtime system to guarantee, and observations made of the system as it runs. Rome is the information model that the Storage Systems Program at HP Laboratories has developed to address these needs. We use it as an ‘information bus’ to tie together our storage system design, configuration, and monitoring tools. In 5 years of development, Rome is now on its third iteration; this paper describes its information model, with emphasis on the QoS-related components, and presents some of the lessons we have learned over the years in using it.