13.1. Backup Fundamentals

To minimize material losses that can stem from losing data, you should know what may cause data loss. In addition, you should analyze the data being backed up to establish how often to back them up and what methods to use for this.

How quickly you recover your system's operability after a data loss depends on how prepared you are for such a development. Using a test system, you have to rehearse all possible situations and work out a recovery process in advance. This will save you the headache of having to learn how to do this when disaster strikes.

To gain a clear understanding of why backup is necessary, consider the following situations that it can alleviate:

Accidentally modifying or deleting files When an inexperienced computer user is connected to a server, his or her often-clumsy actions may result in data loss. With a proper security policy in place, only this particular user 's files are lost, but even they can be of value to the company.
Equipment failure When I was just cutting my teeth in the computer field, 5-inch diskettes and hard drives of no more than 20 MB were used to store information. Although hard drives were sufficiently reliable, diskettes were constantly failing. Switching to 3.5-inch diskettes did not change the situation much, but the reliability of hard drives continued to improve. When the capacity of hard drives started measuring in gigabytes, the bad block problem arose. At one time, I had to change three hard drives , from 10 GB to 20 GB, from different manufacturers. This was like a data-destroying locust incursion. After a certain period of hard drive failures, their reliability began improving. It cannot, however, be called ideal, and there is always a chance of a hard-drive failure.
Natural disasters and equipment loss Many destructive events can cause equipment loss. If you look at the period from the end of 2004 to beginning of 2005, you will notice that natural disasters floods, tornados, earthquakes, hurricanes, tsunamis have been hitting our planet at an increased rate and with a greater intensity. Natural disasters can destroy houses , buildings , and even entire cities, as was the case with New Orleans. You may say that against the background of life and property loss inflicted by such disasters, data loss is insignificant and irrelevant. I disagree , because every little thing salvaged is of help. And if the data lost were accumulated over years , their loss is quite significant.
Hacker and virus attacks These are facts of the information technology field that cannot be ignored and have to be protected against. But no matter what is done to fight viruses, they always have the upper hand. Why is this so? Because the most common defense against viruses is to examine suspicious software for code characteristic to known viruses. The keyword here is known. But hackers constantly keep developing new viruses and ways to get around antivirus software. And it is new viruses that inflict the most damage, because for a certain period after they appear there is no defense against them. Losses inflicted by computer viruses are becoming greater each year. They can, however, be minimized with the help of data backup.

This list can have many items added to it, but I hope I have been able to convince you of the necessity to have a backup copy of all of your important data. I consider important the following types of data:

System configuration files At first, it may seem that these files are not important because they contain no confidential company information. But without such a backup, it will take you a long time to restore your computer or server from scratch. This means losses caused by service unavailability, which for some companies can amount to tens of thousands of dollars for every hour of downtime.
User documents User directories often contain documents of certain value. These are such documents as financial reports or data and specialized user programs.
Databases Corporations keep their data in databases that make the information convenient to work with; should these data be lost, the corporation would suffer greatly.
Web sites Any dynamically developing Web site, from personal to corporate, contains files and scripts, the loss of which can be felt financially .

Database backup depends on the backup tools provided by a particular database. This subject is broad and will not be considered in this book. But most of the theory considered in this chapter can be applied equally well to files and to databases.