On-Line Data Reconstruction in Redundant Disk Arrays

struction, parity declustering, clustered RAID, reconstruction algorithms, RAID. There exists a wide variety of applications in which data availability must be continu-ous, that is, where the system is never taken off-line and any interruption in the accessibil-ity of stored data causes significant disruption in the service provided by the application. Examples include on-line transaction processing systems such as airline reservation sys-tems and automated teller networks in banking systems. In addition, there exist many applications for which a high degree of data availability is important, but continuous oper-ation is not required. An example is a research and development environment, where access to a centrally-stored CAD system is often necessary to make progress on a design project. These applications and many others mandate both high performance and high availability from their storage subsystems. Redundant disk arrays are systems in which a high level of 1/0 performance is obtained by grouping together a large number of small disks, rather than building one large, expensive drive. The high component count of such systems leads to unacceptabl