In this paper, we argue that manageability of file servers is just as important, if not more, as performance. We focus on the design of a self-managing file server and address the specific problem of automating bandwidth allocation to application classes in single-disk and multi-disk servers. The bandwidth allocation techniques that we propose consists of two key components: a workload monitoring module that efficiently monitors the load in each application class and a bandwidth manager that uses these workload statistics to dynamically determine the allocation of each class. We evaluate the efficacy of our techniques via a simulation study and demonstrate that our techniques (i) exploit the semantics of each application class while determining their allocations, (ii) provide control over the time-scale of monitoring and allocation, and (iii) provide stable behavior even during transient overloads. Our comparison with a static allocation technique shows that dynamic bandwidth allocation can yield queue lengths that are 59\% smaller during overloads and admit a larger number of soft real-time clients into the system.