Creating frequent application-consistent backups efficiently

Data can be protected at a production server in a virtually continuous fashion, without necessarily imposing severe constraints on the source application(s). For example, a production server can create an application-consistent backup of one or more volumes, the backups corresponding to a first instance in time. A volume filter driver can monitor data changes in each volume using an in-memory bitmap, while a log file and/or update sequence number journal can keep track of which files have been added to or updated. The volume updates are also consistent for an instance (later) in time. At the next replication cycle, such as every few minutes (however configured), the volume filter driver passes each in-memory bitmap to the physical disk on the production server. The production server then sends the updates to the backup server, which thus stores application-consistent backups for the volume for multiple instances of time.