HERA: Heterogeneous Extension of RAID

A number of recent technological trends have made data intensive applications such as continuous media (audio and video) servers a reality. These servers store and retrieve a large volume of data using magnetic disks. Servers consisting of multiple nodes and large arrays of heterogeneous disk drives have become a fact of life for several reasons. First, magnetic disks might fail. Failed disks are almost always replaced with newer disk models because the current technological trend for these devices is one of annual increase in both performance and storage capacity. Second, storage requirements are ever increasing, forcing servers to be scaled up progressively. In this study we present HERA, a framework that enables parity-based data protection for heterogeneous storage systems. We describe the tradeoffs associated with three alternative HERA techniques: independent subservers, dependent subservers, and disk merging. The novel disk merging approach provides a low cost solution for systems that require highly available secondary storage.