Performance of a distributed storage system with data distributed substantially, evenly across a cluster of storage devices can be dynamically managed of the distributed storage system with respect to performance guarantees to clients of the distributed storage system. Capacity of the distributed storage system in terms of one or more metrics can be determined. This measured capacity can then be compared with allocations of the metric(s) to clients of the distributed storage system. The allocations are determined based on quality of service parameters specified for the clients. The quality of service parameters at least include a maximum value and a minimum value for each of the one or more metrics, and can also include burst credits allocated to the clients. Access to the distributed storage system by the clients can be throttled to ensure the performance guarantees corresponding to the quality of service parameters are fulfilled.