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According to dictionary.com, redundancy is: “The provision of multiple interchangeable components to perform a single function in order to provide resilience (to cope with failures and errors). Redundancy normally applies primarily to hardware. For example, a cluster may contain two or three computers doing the same job. They could all be active all the time thus giving extra performance through parallel processing and load balancing ; one could be active and the others simply monitoring its activity so as to be ready to take over if it failed ("warm standby"); the "spares" could be kept turned off and only switched on when needed ("cold standby"). Another common form of hardware redundancy is disk mirroring.

Redundancy can also be used to detect and recover from errors, either in hardware or software. A well known example of this is the cyclic redunancy  check which adds redundant data to a block in order to detect corruption during storage or transmission. If the cost of errors is high enough, e.g. in a safety-critical system, redundancy may be used in both hardware AND software with three separate computers programmed by three separate teams ("triple redundancy") and some system to check that they all produce the same answer, or some kind of majority voting system.”

Database Redundancy

Redundancy in a database is bad because it takes up memory that does not need to be used and can slow down the operating system.  Redundancy in programs like Microsoft Access is not needed. One way to minimize redundancy is by running database normalization regularly in Microsoft Access. If redundancy is not minimized in your database it is likely that more than one of the same information will show up when searching in your database.

Some problems that can arise when having redundant information in your database include having the same customer, but with two different set of addresses and phone numbers. This is bad because you will not be able to distinguish which field is the most recent and correct information. If you were to have updated the only one field for that customer, you would not have any problems.

Redundancy is not completely bad. It is useful to have whole queries backed up on another hard drive or server, so that if there is a problem with one you will be able to access your information so that you do not have to restart from scratch. This is commonly used for big databases that many people rely on.