backup type

Definition of backup type in The Network Encyclopedia.

What is Backup Type (in computer networking)?

A particular method for performing a backup of files and directories. Each type of backup has a different function in an overall backup plan. Most network backup software (such as Microsoft Windows NT Backup and Windows 2000 Backup) supports five backup methods:

  • Normal backup:
    Backs up everything that is selected to be backed up. Normal backups are the fastest and easiest to restore. Normal backups are sometimes referred to as “full backups.” Use a normal backup when you want to ensure that all your critical system and data files are backed up in a single operation. If your backup cycle consists only of normal backups and you need to perform a restore, you need to use only the most recent normal backup to do so.

     

  • Copy backup:
    Primarily used to produce an additional copy of a backup—for example, a copy to send to the accounting department for monthly archiving and reporting. While a copy backup backs up the same files as a normal backup, there is a difference between the two operations. Performing a normal backup clears the archive bit on each backed up file and marks them as having been backed up. A copy backup, however, does not modify the archive bit on the files backed up. In other words, you can perform a copy backup at any time in a backup cycle without interrupting the cycle in any way—the copy backup is distinct from the backup cycle and is not required when a restore is performed from the cycle’s set of tapes.

     

  • Incremental backup:
    Backs up only files that have been created or modified since the last normal or incremental backup. Files that are backed up in an incremental backup have their archive attributes cleared to indicate that they have been backed up. Using a combination of normal and incremental backups takes less time and uses less storage space than performing only normal backups. However, if you need to perform a restore, you typically need to use the normal backup plus every incremental backup from the current backup cycle to do so.

     

  • Differential backup:
    Copies those files that have been created or changed since the last normal or incremental backup. Files that are backed up by a differential backup do not have their archive attributes cleared, which means that these files will be backed up again in any succeeding differential backups. Differential backups are cumulative with regard to changes—that is, each differential backup in a given backup cycle contains all the files from the last differential backup, plus any files that have been modified since the last differential backup. Thus, if you need to perform a restore, you will typically need to use only the normal backup and the most recent differential backup from the current backup cycle to do so.

     

  • Daily copy backup:
    Copies all files that have been modified on the day the daily copy backup is performed. This method is sometimes used to make a copy of all files a user worked on in a day so that he or she can take them home to work on. Like a copy backup, the daily copy backup does not modify the archive bit of the files backed up; therefore, the daily copy backup does not interrupt the backup cycle in any way.

     

NOTE

Different types of backup operations have different effects on the archive attributes of the files and directories they back up. A backup operation marks the archive attribute by clearing it to indicate that the file has been backed up. If the file is later modified in some way, its archive attribute is set (unmarked). This next table shows what each type of backup operation does to the archive attribute:

Effects of Backup Operations on the Archive Attribute

Backup Type Archive Attribute
Normal
Cleared
Copy
No effect
Incremental
Cleared
Differential
No effect
Daily copy
No effect