A method comprising: queuing, within a storage system, a plurality of I/O requests received by the storage system, wherein the I/O requests are requests to read data from or write data to one or more storage devices (104, 106), the I/O requests including physical characteristics that indicate locations within the one or more storage devices (104, 106) of the data to be read or written; a storage server within the storage system grouping the plurality of I/O requests in a plurality of groups, based upon a logical characteristic associated with certain I/O requests in the plurality of I/O requests, wherein the logical characteristic differs from the physical characteristics; when the storage system is ready to process a pending one of the certain I/O requests that have been queued in the storage system, the storage server selecting a particular I/O request to process based, at least in part, on a policy that specifies that the storage server should allocate load between said certain I/O requests based on respective ratios assigned to each group of the plurality of groups; wherein the storage server selects the particular I/O request, in part, because the particular I/O request belongs to a particular group, of the plurality of groups, and the I/O requests of the particular group already generated an actual load that is furthest behind the particular group's corresponding ratio, as specified by the policy, relative to an actual load in each other group in the plurality of groups; processing the particular I/O request in response to the storage server selecting the particular I/O request. queuing, within a storage system, a plurality of I/O requests received by the storage system, wherein the I/O requests are requests to read data from or write data to one or more storage devices (104, 106), the I/O requests including physical characteristics that indicate locations within the one or more storage devices (104, 106) of the data to be read or written; a storage server within the storage system grouping the plurality of I/O requests in a plurality of groups, based upon a logical characteristic associated with certain I/O requests in the plurality of I/O requests, wherein the logical characteristic differs from the physical characteristics; when the storage system is ready to process a pending one of the certain I/O requests that have been queued in the storage system, the storage server selecting a particular I/O request to process based, at least in part, on a policy that specifies that the storage server should allocate load between said certain I/O requests based on respective ratios assigned to each group of the plurality of groups; wherein the storage server selects the particular I/O request, in part, because the particular I/O request belongs to a particular group, of the plurality of groups, and the I/O requests of the particular group already generated an actual load that is furthest behind the particular group's corresponding ratio, as specified by the policy, relative to an actual load in each other group in the plurality of groups; processing the particular I/O request in response to the storage server selecting the particular I/O request.