Network Data: Types of Backups

You can perform five different types of backups. Many backup schemes rely on full daily backups, but for some networks, using a scheme that relies on two or more of these backup types is more practical.

The differences among the five types of backups involve a little technical detail known as the archive bit. The archive bit indicates whether a file has been modified since it was backed up. The archive bit is a little flag that’s stored along with the filename, creation date, and other directory information.

Any time a program modifies a file, the archive bit is set to the On position. That way, backup programs know that the file has been modified and needs to be backed up.

The differences among the various types of backups center around whether they use the archive bit to determine which files to back up as well as whether they flip the archive bit to the Off position after they back up a file. The following table summarizes these differences.

Backup programs allow you to select any combination of drives and folders to back up. As a result, you can customize the file selection for a backup operation to suit your needs.

For example, you can set up one backup plan that backs up all a server’s shared folders and drives plus its mail server stores but then leaves out folders that rarely change, such as the operating system folders or installed program folders. You can then back up those folders on a less regular basis. The drives and folders that you select for a backup operation are collectively called the backup selection.

How Backup Types Use the Archive Bit
Backup Type Selects Files Based on Archive Bit? Resets Archive Bits After Backing Up?
Normal No Yes
Copy No No
Daily No* No
Incremental Yes Yes
Differential Yes No

*Selects files based on the Last Modified date.