US Patent 10268419 Quality of service for storage system resources

A hierarchy of multiple levels of storage resources and associated QOS (quality of service) limits and buckets of tokens may be specified. A different QOS limit may be applied to each individual storage resource. The buckets may denote current amounts of tokens available for consumption in connection with servicing I/O operations. Each bucket may denote a current amount of available tokens for a corresponding storage resource of included in the hierarchy. Processing may include receiving a first I/O operation directed to a first storage resource, and determining, in accordance with the buckets of available tokens, whether to service the first I/O operation.