1. A method comprising performing a machine-executed operation involving instructions for managing shared storage input-output (I/O) resources, wherein said instructions are instructions which, when executed by one or more processors, cause the one or more processors to perform certain steps comprising: receiving a request for an I/O operation on a storage system; determining an I/O rate at which I/O operations have recently issued to said storage system for an I/O scheduling group with which said request is associated; determining, based at least in part on said I/O rate and on an I/O policy associated with said I/O scheduling group, whether to place said request in an I/O request queue; if determined to place said request in an I/O request queue, then placing said request in a particular I/O request queue associated with said I/O scheduling group; and issuing said request to said storage system when said request is dequeued from said particular I/O request queue based on said I/O policy, for performance of said I/O operation by said storage system; wherein the machine-executed operation is at least one of (a) sending said instructions over transmission media, (b) receiving said instructions over transmission media, (c) storing said instructions onto a machine-readable storage medium, and (d) executing the instructions.