We propose a fluid model for eMule-like file sharing systems. The analytical analysis of a two file system is presented followed by the numerical analysis of a n-file system. We show the influence of the parameters such as the storage probability of a file and the request rate for a file on the system performance, i.e., on average downloading times. Our results reveal that the uploading policy, which equally treats each request, is not appropriate and that it introduces unfairness in the system. Afterwards, we discuss the optimal uploading policy on peers, i.e., which part of the uploading bandwidth should be dedicated to each shared file on a peer in order to improve the fairness in the system.