12.1 Backup Strategies
12.1.1 Importance of backups
Good backups are critical to the health of a network. The value of a good backup system is most appreciated when it is needed in an emergency. When a system is down and data becomes unavailable, people are unable to get their work done and companies are unable to do business.

A well-managed network includes regular backups performed by a system administrator. Network administrators who do not have good backups or are unable to restore data quickly may lose their jobs because of it. Having a good backup system and a tested restoration process can save an organization millions of dollars and thousand of hours in lost productivity. Data can be lost or corrupted due to many things, including:

Hard Disk Failure - Disk drives (floppy, Hard disks and CDs) are the most likely components in a computer to fail since they are electromechanical devices with moving parts that wear. Most other components in a computer, such as the CPU and RAM, are electronic with no moving parts. When a hard drive fails, some or all of the data on the drive can be damaged or become inaccessible. This is why fault tolerant disk systems such as RAID 5 (Redundant Array of Independent Disks - Level 5) were developed for network servers. RAID 5 combines three or more drives as a group so that if one fails, the others take over. The bad drive can be replaced with no loss of service to the users. Another fault tolerant technique is mirroring, which uses two drives with the second drive storing the same data as the first. One of the drives can fail and the other will take over. Fault tolerant disk systems are the first line of defense in a solid backup strategy.

File Corruption - File corruption can occur due to many things including improper system shutdown, magnetic fields near the data or when an area of the disk goes bad. In any case, the data becomes inaccessible. A good backup system will allow the administrator to find and recover a specific file.

Malicious Destruction - Files can also be lost due to intentional destruction of data. File deletion can result from disgruntled employees, virus attacks, or hackers who can remotely access a system. Damage can vary from deletion of one or two files to the loss of all data on a hard drive. Most virus attacks come from the Internet and firewalls can help in some cases. Fortunately, UNIX is relatively immune to virus attacks, but most other network operating systems and desktop operating systems are not. For non-UNIX operating systems, virus protection software can be installed to help detect and eradicate viruses before they do damage. Firewalls can also help in the case of hackers by detecting and blocking the attacks. In the case of a disgruntled employee deleting data, the best defense is having a good backup.

Disasters - Disasters such as fires and floods can destroy computers, data centers, and entire buildings. In the previous chapter on security, we discussed the importance of a disaster recovery plan. If a fire were to destroy a place of business, how would they recover? How much would it cost them per day or per hour to not be able to do business? Backups are a big part of a disaster recovery plan. To get systems back up and running quickly, it is important to have good quality current backups of critical data. The backups should also contain copies of operating system and applications software and should be stored offsite at a nearby location.

Accidental Deletion / Overwrite - It is not uncommon for a user to accidentally delete a file. Files deleted from the command line cannot be recovered except from a backup. If the file cannot be recovered from a backup, it may need to be recreated causing lost productivity. Files deleted using CDE File Manager can be recovered from the Trash Can. Work can also be lost due to accidental overwrites. This occurs when a user makes a copy of a file and then makes substantial changes to it. They then open the original file and save it over the one with changes. It is also possible to overwrite files when copying them from one location to another where the file already exists. When this occurs the only way to recover the original file is from data backups.