An incremental backup is a type of strategy that is often chosen by information technology administrators, owners of a home-based business and users of personal computers to preserve the existence and integrity of data. When only the changes that have occurred in user data files or files that make up a system are backed up, it is called an incremental backup. The changes are the "increments." This is a form of continuous data protection so that system restoration can be performed in the event of a system failure and accidental deletion of data. System restoration is made possible by using the media on which copies of the needed data were stored via implementation of the incremental backup strategy.
Files that change on a system can be those that are produced with programs. For example, when someone writes and saves a letter using word processing software, he or she creates what generally is known as user data or user files. Changes can also be made to the files that make up the operating system itself as well as to the files of the software programs that run under it. Although an incremental backup strategy might be chosen by someone who is responsible for continuous data protection, it is almost always combined with the periodic performance of a full system backup.
Administrators of medium-to-large systems typically choose to do a daily incremental backup to preserve the data that has changed or that has been created, along with a weekly backup of the entire system. There are different versions of this type of strategy, and each version has advantages and disadvantages. One version involves having each incremental backup reference the original full system so that system restoration would require only the media holding the full system and the most recent incremental backup. If the data is being backed up to tapes, this would mean working with just two tapes to recover from a system failure. The disadvantage to this version of an incremental backup generally is seen in heavily used systems in which there are numerous files that could be very large in size.
Another version of this type of backup strategy involves having the increments reference previous increments instead of the full system. Although this strategy requires less time because there is less data on each tape or type of backup media chosen, it is not without disadvantages. A full system restoration would require working with more than two sets of data. It would require the running of every set of user files, system files and all changes to them since the loss of data.