Ensuring Performance in Activity-Based File Relocation

Dynamic storage tiering (DST) is the concept of grouping storage devices into tiers based on their characteristics, and relocating files dynamically to leverage on the heterogeneity of the underlying devices. An important usage of DST is activity-based file relocation, where less active files can be stored on less expensive devices without affecting the overall perceived quality of the storage system. In activity-based file relocation, improper choices on how much activity a file should have before it is relocated introduce the potential for overcommitting the performance capability of the preferred tier. We present an approach to prevent performance degradation caused by excessive skewing of loads. Our approach enables the delineation of periods when performance requirements are different. We consider the load pattern of files and limit the total amount of loads to be placed on the preferred tier during the periods when fast response time is desirable, and increase the load limit in other periods when throughput is more important. Considering the variation of performance requirements in time enables the finer attainment of QoS goals.