Delta differencing (also called "delta differential") is a backup technique used to make the process more efficient. The process involves examining a backup file set and locating the blocks or bytes that have changed since the last backup period. Changed data, rather than the entire file set, can then be sent to the backup target locally across the LAN (local area network) or to a virtual tape library (VTL) or other remote storage across the WAN (wide area network).
The major benefit of delta differencing is time savings. Most enterprise data sets change by only a small percentage each day. Although complete backup is essential place to start, it's typically cumbersome and time-consuming. For this reason, many organizations defer complete backups to the weekends, which leads to an unacceptably large recovery point objective (RPO). By gathering and saving only the changed data, it is possible to perform much faster and more frequent backup cycles without monopolizing the LAN or WAN bandwidth. Smaller backup portions also use storage space far more efficiently, foregoing the many file duplications that waste space in repeated full backups.
For example, a data center with several terabytes of storage may only change by a few gigabytes each day. While a complete backup of the data center may take many hours (even days), a delta differencing backup can update the complete backup with any daily changes in only a few minutes or hours.