Performance of a storage system with data distributed substantially, evenly across a cluster of storage nodes can be dynamically managed according whether quality of service (QoS) rules based on one or more performance capacities according to performance class is satisfied, wherein each QoS rule includes a boundary condition and a threshold expressing performance guarantees to a respective performance class. Determining for each QoS rule, whether a respective boundary condition satisfies a respective threshold based on measured capacity for a performance metric corresponding to the respective boundary condition; and if so, setting a first QoS parameter associated with the set of QoS rules and throttling access to the storage system by a first client associated with a first performance class based on the first QoS parameter to enforce the performance guarantees to the first performance class.