US Patent 10552051 Allocation of heat-tiered storage among throttling units

A data storage system has multiple tiers of data storage including an upper tier having a lower access latency and a lower tier having a higher access latency. A storage controller of the data storage system implements throttling limits regulating access to data in the data storage system for a plurality of throttling units sharing the data storage system. The storage controller also tracks access frequencies of extents in the data storage system. The storage controller migrates extents among the multiple tiers based on the access frequencies of the extents and the throttling limits implemented for the throttling units.