8.2.3.2. Incremental Backups

Unlike full backups, incremental backups first look to see whether a file's modification time is more recent than its last backup time. If it is not, the file has not been modified since the last backup and can be skipped this time. On the other hand, if the modification date is more recent than the last backup date, the file has been modified and should be backed up.

Incremental backups are used in conjunction with a regularly-occurring full backup (for example, a weekly full backup, with daily incrementals).

The primary advantage gained by using incremental backups is that the incremental backups run more quickly than full backups. The primary disadvantage to incremental backups is that restoring any given file may mean going through one or more incremental backups until the file is found. When restoring a complete file system, it is necessary to restore the last full backup and every subsequent incremental backup.

In an attempt to alleviate the need to go through every incremental backup, a slightly different approach was implemented. This is known as the differential backup.