Data organization in a hybrid storage system

Flash memory based Solid State Devices (SSDs) have become commercially viable and hybrid storage systems incorporating SSDs and magnetic disk drives are being built. There are a number of ways the data can be organized in such hybrid systems. SSDs can be organized at a higher layer as a cache in a transparent hierarchy. SSDs can be organized as peers to magnetic disks in a heterogeneous storage system. There are pros and cons for organizing data in both approaches. This paper argues that a storage system with SSDs and disk drives as peers may deliver the best performance, with maximum flexibility.