Difference between Differential and Incremental Backup

Differential vs Incremental Backup

It is important to understand what is meant by both differential backup and incremental backup, before discussing their pros and cons. As the name would suggest, both of these methods are ways in which the computer backs up data in a smart way. In backing up data, both of these ways help to save time and disk space which is of high importance. What stands out in the incremental backup feature is that only files that have been changed are backed up, saving time and disk space. The overall result of how data is backed up and the usefulness of the method may vary depending on the size of the database.

As has been noted, it is important to ensure that only data that has been changed is backed up for the sake of speed and the amount of computer resources needed. Differential and incremental backups are two different means by which data can be backed up. To backup the data, the two methods rely on use of a basic on / off attribute called the archive bit. This is the element that takes note of the data that has been backed up. The file property of a given file when checked should show whether or not the archive bit has been checked or unchecked.

In the event that the archive bit has been checked, or set, it indicates that a file needs to be backed up. If unchecked, or cleared, it means the file in question does not need to be backed up. If the archive bit is left unchecked, the operating system automatically checks the archive bit of any modified file that may have not been checked. When a full backup is performed, all the archive bits of the files in the system are set to ‘off’ by default as all their archive bits have been backed up. This means that whether the archive bit of a given file was on or off, they are backed up.

Differences

In an incremental backup, only files which have their archive bit set on are backed up, after which the archive bit is set to ‘off’. This in effect results in only files that have been changed being backed up. The biggest advantage of the incremental backup is that it is economical in space and resources use when compared to the differential backup method.

The differential backup on the other hand will also backup the selected data files which have their archive bit set on or checked, but this backup method is different in that it does not clear, or uncheck, the archive bit. This means that it backs up new files and all other files that had their archive bits selected. This means that when you need to restore backed up files you will get a comprehensive restoration. To restore backed up files with incremental backups, on the other hand, would require the use of all incremental backups that have been done since the last full backup.

The speed of the backups is also a crucial difference, as differential backups are quite fast as opposed to incremental backups when there is not a lot of data being backed up. However, as the database grows, the speed of differential backups decreases. Incremental backups become more desirable than differential backups when dealing with large databases, as only the changed files are backed up.

Summary

Incremental backup only backs up data that has their archive bit set on. Upon backing up, the archive bit is set off.  

Differential backups will save data that have their archive bit set on and when done does not set it off.

Differential backups are faster than incremental backups for small databases.

Incremental backups are more beneficial for larger data sets.

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