Consistent data versus current or up-to-date data

Data is consistent if the system or application using it can be successfully restarted to a known, usable state. The data on the Secondary is consistent if it correctly reflects the data on the Primary at some point in the past. At all times, VVR maintains the data at the Secondary in a consistent state with the data at the Primary. For example, if the data being replicated is used by a database, the data is consistent if the database can be started and recovered to a usable state with zero data corruption. If the data contains a file system, the data is consistent if the file system check utility can be run and it can recover with no file system corruption.

Data is considered consistent only if it contains all updates up to a point in time and none of the updates that come after that point. For example, if it is a file system, the most recently created files may be missing when it is restarted. Or, if it is a database, one or more of the most recently committed transactions might be missing.

Data that is current or up-to-date contains the latest changes made at the Primary. For example, if you are replicating a database, the most recent transaction is available at the Secondary. Whether or not the data on the Secondary must always be current is a business decision and can be controlled by choosing between synchronous and asynchronous modes of replication.