incremental backup

(operating system)

A kind of backup that copies all files which have changed since the date of the previous backup. The first backup of a file system should include all files - a "full backup". Call this level 0. The next backup could also be a full level 0 backup but it is usually much quicker to do a level 1 backup which will include only those files which have changed since the level 0 backup. Together the level 0 and level 1 backups will include the latest version of every file. Level 1 backups can be made until, say, the backup tape is nearly full, after which we can switch to level 2. Each level includes those files which have changed since the last backup at a lower level. The more levels you use, the longer it will take to restore the latest version of a file (or all files) if you don't know when it was last modified.

Compare differential backup.

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backup types

There are two categories of backup: system backup and file backup. System backup copies everything verbatim on the hard drive onto an external storage medium, including the operating system, applications and data. If the drive fails, the computer can be restored to its former state.

File backup copies only data files onto an external storage medium. If the drive fails, the OS and applications have to be re-installed. Following are the various types.

Full and Differential Backups
A full backup copies all selected files. A differential backup copies only files that have changed since the last backup.

Incremental and Delta Backups
When each revision of a file must be maintained, an incremental backup appends selected files to the backup medium and does not replace existing backup files. A delta backup is similar to an incremental backup but copies only the changed data within the selected file, not the entire file (it backs up the differences). See deduplication, backup software and cloning software.

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