The duplication of data on a number of computers within a distributed system. There are three main reasons for data replication. The first is that computers malfunction and go out of service; if only one computer held a single copy of an important set of data, then this would become immediately unavailable. Data replicated across a number of computers eliminates this problem. A second reason is to increase access time. Data can take a long time to travel over large computer networks, particularly wide area networks. In order to achieve fast response times, such data is often replicated in computers that are close to those which access it: for example, the data might be contained on a computer which is connected via a local area network. A third reason is to provide a backstop to guard against data being affected by an attack which may, for example, delete it.