The design of a file system has never been a simple nor a straightforward task because of its complexity. Heuristics and experience still play a major role in guiding the design process. To organize the entire design process in a more systematic manner, large scale simulation has proved to be an effective technique. The FOREM models developed during the past several years (specifically for the evaluation of file system designs) represent facilities of this type. This paper utilizes the FOREM model as the principal tool and presents a hypothetical design example dealing with many essential issues of the design process. Evaluation of designs of several other actual file systems are also being carried out and will be reported at a later date. Only through quantitative evaluation can each design decision be arrived at correctly and the possible tradeoffs be identified.