Advanced functions for storage subsystems: Supporting continuous availability

Storage subsystems must support advanced copy functions. In particular, these functions are needed to enable the subsystem to support disaster recovery. Continuous remote copy functions ensure that all data written to a primary control unit are also written to a remote secondary control unit that, it is assumed, will not be impacted by a disaster. There are many variants of continuous remote copy, and it can be implemented in many ways and at various levels, including the application, the file system, and the disk storage subsystem. Although we mention other levels, our focus is on the storage subsystem. In this paper, we describe the variants of continuous remote copy and their implementation, emphasizing Peer-to-Peer Remote Copy (PPRC) supported by the IBM TotalStorage™ Enterprise Storage Server® (ESS).