It is a known fact that every electrical or mechanical device will sooner or later fail; therefore, it is not so much a question of whether it will fail, but when it will fail. Database professionals must willing accept this fact in order to fully comprehend the necessity for functional backups. The principle of backups, when compared to a real life situation, is easily understood. For example, if a person wants to call a business associate they must first retrieve the number from a directory. In this case, one type of directory could be the person's brain or, better yet, a mental directory. However, suppose for a moment that the telephone number has been forgotten or lost from the directory, the brain as a mental directory becomes useless. Therefore, the person has to look elsewhere to find the information. The person's Rolodex, the phone book or even the telephone company's directory assistance can all be considered backups to the mental directory that held the business associate's phone number. A system such as this is virtually foolproof; at least one of the backup sources will allow the person to retrieve the needed information. When put into this perspective, it is easily understood why backups play such an important role in any business. .
To classify the previous analogy in a way that means something to computer-minded professionals, consider the Rolodex as the "on-site incremental backup", the phone book as the "on-site full backup," and the directory assistance as the "off-site full backup" (Nelson). These types of backups are the strategies that have been practiced by companies for years to prevent against the loss of data. The most common backup strategy is the full backup. A full backup requires that every file on the local file system be backed up, whether changed or not, consequently, causing the process of full backups to become very time consuming. Since the full backup is so time intensive, most companies conduct it during weekends.
