On-Line Data Reconstruction In Redundant Disk Arrays

There exists a wide variety of applications in which data availability must be continuous, that is, where the system is never taken off-line and any interruption in the accessibility of stored data causes significant disruption in the service provided by the application. Examples include on-line transaction processing systems such as airline reservation systems 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 operation 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 I/O performance is obtained by grouping together a large number of small disks, rather than building one lar..