ABSTRACT
Since almost the inception of the computer industry—at least its adoption in business—an ever-increasing goal has been high availability. Availability refers to the period of time the system is reachable, or contactable. Storage virtualization systems offering effective continuous data availability should not be confused with synchronous replication. While synchronous replication mirrors many of the features of continuously available virtualized storage, there is usually an assumption of an (even brief) outage in the event of the primary storage target experiencing a failure. Continuous data protection (CDP) is an evolutionary growth beyond replication (and primarily, asynchronous replication). Whereas the purpose of replication is to get the secondary copy “up to date” either immediately or eventually, CDP provides a functionality more akin to a digital video recorder: providing a copy, but also allowing people to rewind seconds, minutes, or even longer to an earlier version of the replicated content.
