Incremental Backups

An incremental backup contains only data that is new or has changed since the last backup, regardless of the type. On average, incremental backups consume far less media and place less of a burden on resources than full backups.

The following figure shows the nature of full and incremental backups. For simplicity, assume there is a file system that contains six files. Note that the file system could also represent other data such as database tables, Active Directory objects and attributes.

Backup #1 is a full backup and therefore writes all the data, changed and unchanged, to the backup media. Backups #2 through #n-1 are incrementals and only back up those files that have changed since the time of the last backup, regardless of the type. For example, files A, B, and E changed after the full backup and were therefore backed up in Backup #2. Backup #4 backed up files A and D because both files were modified sometime after Backup #3 occurred. File F did not change; therefore it was not backed up in any of the incremental backups, but it was included in both full backups, which, by definition, back up everything.