What is DIFFERENTIAL BACKUP? What does DIFFERENTIAL BACKUP mean? DIFFERENTIAL BACKUP meaning - DIFFERENTIAL BACKUP definition - DIFFERENTIAL BACKUP explanation.
Source: Wikipedia.org article, adapted under https://creativecommons.org/licenses/by-sa/3.0/ license.
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A differential backup is a type of data backup that preserves data, saving only the difference in the data since the last full backup. The rationale in this is that, since changes to data are generally few compared to the entire amount of data in the data repository, the amount of time required to complete the backup will be smaller than if a full backup was performed every time that the organization or data owner wishes to back up changes since the last full backup. Another advantage, at least as compared to the incremental backup method of data backup, is that at data restoration time, at most two backup media are ever needed to restore all the data. This simplifies data restores as well as increases the likelihood of shortening data restoration time.
A differential backup is a cumulative backup of all changes made since the last full backup, i.e., the differences since the last full backup. The advantage to this is the quicker recovery time, requiring only a full backup and the last differential backup to restore the entire data repository. The disadvantage is that for each day elapsed since the last full backup, more data needs to be backed up, especially if a significant proportion of the data has changed, thus increasing backup time as compared to the incremental backup method.
It is important to use the terms "differential backup" and "incremental backup" correctly. The two terms are widely used in the industry, and their use is universally standard. A differential backup refers to a backup made to include the differences since the last full backup, while an incremental backup contains only the changes since the last incremental backup. (Or, of course, since the last full backup if the incremental backup in questions is the first incremental backup immediately after the last full backup.) All the major data backup vendors have standardized on these definitions, including Microsoft, Acronis, and Symantec.
Microsoft, makers of Backup and Restore, defines incremental backups and differential backups as follows: "Incremental: An incremental backup provides a backup of files that have changed or are new since the last incremental backup....Differential: A differential backup provides a backup of files that have changed since a full backup was performed. A differential backup typically saves only the files that are different or new since the last full backup, but this can vary in different backup programs. Together, a full backup and a differential backup include all the files on your computer, changed and unchanged." Microsoft products, such as Exchange Server 2010 use this definition in their literature and support sites.
Acronis, makers of Acronis True Image, states that “A differential backup backs up only the files that changed since the last full back...Incremental backups also back up only the changed data, but they only back up the data that has changed since the last backup — be it a full or incremental backup.”
MySQL, makers of MySQL Enterprise Backup, states that "An incremental backup only backs up data that changed since the previous backup ."
CA Technologies, makers of ArcServe, states that “Incremental Backup…backs up the… files that have changed since the last backup. Differential Backup… backs up …files that have changed since the last full backup.”
Symantec, makers of Backup Exec, states that “An Incremental backup backs up only the selected files that have their archive bit set to ON, setting them back to OFF. This results in a backup of all files that are new or changed since the last backup, whether it was a full or an incremental...A Differential backup will back up all selected files that are new and changed since the last full backup.”