Evaluation of Placement and Access Asignment for Replicated Object Striping

The number of stored objects that should be targets of high throughput retrieval, such as multimedia stream objects, is increasing recently. To implement a high throughput storage system, striping technique using multiple disk drives are commonly used. However, the ordinary disk striping methods implemented in RAID 0, 3-5 have problems of the flexibility, extensibility, and quality of services (QoS). We have proposed the autonomous disk cluster to realize the flexible and extensible storage system by treating each target object as a unit for management. It also adopts the primary-backup technique for the object to satisfy required QoS. We have shown that the autonomous management for the object unit is effective. However, there is room for improving its throughput. In this paper, we consider an approach for importing a flexible striping technique into the autonomous disk system to provide high throughput. It is important to locate fragments of an object into a part of disk cluster appropriately with considering workload skews to derive the required throughput. We use access history to decide their location. We also propose a method to divide access load into fragmented primary and backup adaptively. The experimental results using PC cluster indicate that the proposed methods are effective.