A complete backup is a full backup of the entire server or PC client hard drive. For a server, this includes all volumes, directories, and files. For a PC client, this includes all drives, directories, and files.
A partial backup can be any of the following:
Differential - Copies all files that were changed since the last complete backup. Differential backups are useful when it is important to have the latest version of each file. If the same media is used for consecutive differential backups, the newer versions of backed up files are often allowed to overwrite older versions of the same file. Typically, backup programs do not reset the file's archive bit after a differential backup, the archive bit remains turned on until the next complete backup.
Incremental - Copies all files that were changed since the last backup. This type of backup is used when each revision of a file must be maintained. If the same tapes are used for consecutive incremental backups, the newer versions of backed-up files are not allowed to overwrite earlier versions. Rather, the newer files are usually appended to the backup medium. Typically, backup programs reset the archive bit following each incremental backup.
User-defined - Copies a user-defined set of files. Often this is a special backup requested by a group of employees on a mission-critical project.
Clearly the amount of backed-up information varies with the type of backup selected. No matter which method that you choose, NAS, External Drive, DVD's, follow a schedule and periodically verify all backups have completed successfully.