Issues in disaster recovery

The increased demand in recent years for continuous operation of databases has created interest in remote backups, which allow systems to continue their operation, even in the presence of disasters. The motivation for remote backups and their applicability to various systems are discussed. A remote backup can ensure continuous operation, even in the presence of extensive failures that may render an entire site inoperational and for which local replication may be inadequate. In particular, the geographic separation of two copies helps isolate failures that might otherwise affect the backup copy, as well as the primary. Some of the issues involved in the design, implementation, and evaluation of remote backup mechanisms are presented. Consistency is a major interest for remote backups: a recovery mechanism may produce either a consistent backup copy or an inconsistent one. Consistency will be highly desirable in most cases, since application programs are usually written under the assumption that they will operate on correct data, and error handling in these programs is rarely comprehensive. Some criteria that can be used for evaluating and comparing various remote backup mechanisms are presented. Topics discussed are taxonomy, implementation choices, and comparison metrics.<>