A complete backup strategy should balance the probability of a problem occurring with the amount of data that would be lost in a given situation, with the amount of time and resources spent on backups. A disk failure is a more likely event than a fire or a flood. To reduce cost of data loss in the event of disk failure, you should have redundancy at the disk level. A fire or flood is less likely, and it is understood that some data would be lost should such an event occur.
It is important to include the users in the disaster-planning process. They are the real owners of the data, and can provide input to help decide the probability/data loss/cost trade-offs. It is sometimes helpful to put a price on lost data and downtime because it makes it easier to do the final cost/benefit analysis.
While it is possible to provide near-100-percent reliability, there is a large cost. For example, an emergency services organization needs as close to 100 percent reliability as possible, since a failure on its part could cost lives. It must have complete, duplicate systems at a second location, with available staff in case the primary location is knocked out by a disaster. Your situation might allow you to lose some data and availability of the system in exchange for lower cost. It is important to focus on the entire system and not just your databases and applications—you must also weigh the cost/benefit of each strategy.
The sections that follow identify the key questions to ask when developing a complete backup-and-recovery strategy.
