Replication has the potential to improve both availability and performance in the Web. An increasingly important special-case for availability is mobile computing. A portable computer is often intentionally disconnected from the network. Although a number of wireless approaches to communications have been proposed, but cost and geography often prevent their use. Data replication on portable computers can again address this availability problem.
Performance is the other major motivation for replication.
Even when wireless networking is both affordable and available, bandwidth may be less than is required. Data replicated on the local disk is immediately accessible. Performance over wide-area networks is also a concern. Even when bandwidth is available, the speed of light requires about 30ms to cross the United States and nearly 300ms if via satellite. In these cases access to a closer replica can substantially improve performance.