In computer
main memory,
auxiliary storage and
computer buses, data redundancy is the existence of data that is additional to the actual data and permits correction of errors in stored or transmitted data. The additional data can simply be a complete copy of the actual data (a type of
repetition code), or only select pieces of data that allow
detection of errors and reconstruction of lost or damaged data up to a certain level.
For example, by including computed check bits,
ECC memory
Error correction code memory (ECC memory) is a type of computer data storage that uses an error correction code (ECC) to detect and correct ''n''-bit data corruption which occurs in memory.
Typically, ECC memory maintains a memory system immun ...
is capable of detecting and correcting single-bit errors within each
memory word, while
RAID 1 combines two
hard disk drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...
s (HDDs) into a logical storage unit that allows stored data to survive a complete failure of one drive. Data redundancy can also be used as a measure against
silent data corruption; for example,
file systems such as
Btrfs and
ZFS use data and
metadata
Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive ...
checksumming in combination with copies of stored data to detect silent data corruption and repair its effects.
In database systems
While different in nature, data redundancy also occurs in
database systems that have values repeated unnecessarily in one or more records or
fields, within a
table, or where the field is replicated/repeated in two or more tables. Often this is found in
unnormalized database designs and results in the complication of database management, introducing the risk of corrupting the data, and increasing the required amount of
storage. When done on purpose from a previously normalized database schema, it ''may'' be considered a form of
database denormalization; used to improve performance of database queries (shorten the database response time).
For instance, when customer data are duplicated and attached with each product bought, then redundancy of data is a known source of
inconsistency since a given customer might appear with different values for one or more of their attributes.
Data redundancy leads to
data anomalies and corruption and generally should be avoided by design;
applying
database normalization prevents redundancy and makes the best possible usage of storage.
See also
*
Data maintenance
*
Data deduplication
*
Data scrubbing
*
End-to-end data protection
*
Redundancy (engineering)
In engineering and systems theory, redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve a ...
*
Redundancy (information theory)
Redundancy or redundant may refer to:
Language
* Redundancy (linguistics), information that is expressed more than once
Engineering and computer science
* Data redundancy, database systems which have a field that is repeated in two or more tab ...
References
{{DEFAULTSORT:Data Redundancy
Computer memory
Data
Data modeling
Databases
Fault-tolerant computer systems