A traditional backup starts with an initial full backup and is followed by a series of incremental or cumulative incremental backups (also known as differential backups). After some period of time, you will perform another full backup and more incremental backups. However, the advent of disk-based backup systems has given rise to the concept of the incremental forever approach, where only one backup is performed followed by a series of incremental backups. Let’s take a look at the different ways to do this.
File-level incremental forever
The first type of incremental forever backup is a file-level incremental forever backup product. This type of approach has actually been around for quite some time, with early versions of it available in the ‘90s. The reason why this is called a file-level incremental is that the decision to backup an item happens at the file level. If anything within a file changes, it will change its modification date (or archive bit in Windows), and the entire file will be backed up. Even if only one byte of data was changed within the file, the entire file will be included in the backup.
Source:: Network World – Data Center