1. A computer-implemented method at a data storage system comprising: accessing, at a processor, a policy comprising one or more criteria to be applied to a flow of data storage input/output requests between endpoints of the flow, the endpoints comprising at least one computing entity and at least one store; sending control instructions to at least one stage of the flow of data, the stage being a component of the data storage system through which the flow passes and which is configured to interpret the control instructions, the control instructions arranged to control a plurality of queues at the at least one stage in order to treat the flow of data storage input/output requests such that the policy is met.