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Data degradation is the gradual corruption of computer data due to an accumulation of non-critical failures in a data storage device. It is also referred to as data decay, data rot or bit rot. [1] This results in a decline in data quality over time, even when the data is not being utilized.
Data degradation in dynamic random-access memory (DRAM) can occur when the electric charge of a bit in DRAM disperses, possibly altering program code or stored data. DRAM may be altered by cosmic rays [2] or other high-energy particles. Such data degradation is known as a soft error. [3] ECC memory can be used to mitigate this type of data degradation. [4]
Data degradation results from the gradual decay of storage media over the course of years or longer. Causes vary by medium:
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Below are several digital images illustrating data degradation, all consisting of 326,272 bits. The original photo is displayed first. In the next image, a single bit was changed from 0 to 1. In the next two images, two and three bits were flipped. On Linux systems, the binary difference between files can be revealed using cmp command (e.g. cmp -b bitrot-original.jpg bitrot-1bit-changed.jpg).
This deterioration can be caused by a variety of factors that impact the reliability and integrity of digital information, including physical factors, software errors, security breaches, human error, obsolete technology, and unauthorized access incidents. [12] [13] [14] [15]
Most disk, disk controller and higher-level systems are subject to a slight chance of unrecoverable failure. With ever-growing disk capacities, file sizes, and increases in the amount of data stored on a disk, the likelihood of the occurrence of data decay and other forms of uncorrected and undetected data corruption increases. [16]
Low-level disk controllers typically employ error correction codes (ECC) to correct erroneous data. [17]
Higher-level software systems may be employed to mitigate the risk of such underlying failures by increasing redundancy and implementing integrity checking, error correction codes and self-repairing algorithms. [18] The ZFS file system was designed to address many of these data corruption issues. [19] The Btrfs file system also includes data protection and recovery mechanisms, [20] as does ReFS. [21]
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
Disk storage is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism. Notable types are hard disk drives (HDD) containing one or more non-removable rigid platters, the floppy disk drive (FDD) and its removable floppy disk, and various optical disc drives (ODD) and associated optical disc media.
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communication channels. Many communication channels are subject to channel noise, and thus errors may be introduced during transmission from the source to a receiver. Error detection techniques allow detecting such errors, while error correction enables reconstruction of the original data in many cases.
RAID is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This is in contrast to the previous concept of highly reliable mainframe disk drives referred to as "single large expensive disk" (SLED).
In computing, a block, sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size. Data thus structured are said to be blocked. The process of putting data into blocks is called blocking, while deblocking is the process of extracting data from blocks. Blocked data is normally stored in a data buffer, and read or written a whole block at a time. Blocking reduces the overhead and speeds up the handling of the data stream. For some devices, such as magnetic tape and CKD disk devices, blocking reduces the amount of external storage required for the data. Blocking is almost universally employed when storing data to 9-track magnetic tape, NAND flash memory, and rotating media such as floppy disks, hard disks, and optical discs.
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Reading is an action performed by computers, to acquire data from a source and place it into their volatile memory for processing. Computers may read information from a variety of sources, such as magnetic storage, the Internet, or audio and video input ports. Reading is one of the core functions of a Turing machine.
Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data. Computer, transmission, and storage systems use a number of measures to provide end-to-end data integrity, or lack of errors.
Density is a measure of the quantity of information bits that can be stored on a given length of track, area of the surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows more data to be stored in the same physical space. Density therefore has a direct relationship to storage capacity of a given medium. Density also generally affects the performance within a particular medium, as well as price.
Data remanence is the residual representation of digital data that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal file deletion operation, by reformatting of storage media that does not remove data previously written to the media, or through physical properties of the storage media that allow previously written data to be recovered. Data remanence may make inadvertent disclosure of sensitive information possible should the storage media be released into an uncontrolled environment.
Write once read many (WORM) describes a data storage device in which information, once written, cannot be modified. This write protection affords the assurance that the data cannot be tampered with once it is written to the device, excluding the possibility of data loss from human error, computer bugs, or malware.
Preservation of documents, pictures, recordings, digital content, etc., is a major aspect of archival science. It is also an important consideration for people who are creating time capsules, family history, historical documents, scrapbooks and family trees. Common storage media are not permanent, and there are few reliable methods of preserving documents and pictures for the future.
In computing, data recovery is a process of retrieving deleted, inaccessible, lost, corrupted, damaged, or formatted data from secondary storage, removable media or files, when the data stored in them cannot be accessed in a usual way. The data is most often salvaged from storage media such as internal or external hard disk drives (HDDs), solid-state drives (SSDs), USB flash drives, magnetic tapes, CDs, DVDs, RAID subsystems, and other electronic devices. Recovery may be required due to physical damage to the storage devices or logical damage to the file system that prevents it from being mounted by the host operating system (OS).
Data scrubbing is an error correction technique that uses a background task to periodically inspect main memory or storage for errors, then corrects detected errors using redundant data in the form of different checksums or copies of data. Data scrubbing reduces the likelihood that single correctable errors will accumulate, leading to reduced risks of uncorrectable errors.
etree, or electronic tree, is a music community created in the summer of 1998 for the online trading of live concert recordings. etree pioneered the standards for distributing lossless audio on the net and only permits its users to distribute the music of artists that allow the free taping and trading of their music.
Error correction code 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.
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, or only select pieces of data that allow detection of errors and reconstruction of lost or damaged data up to a certain level.
Predictive Failure Analysis (PFA) refers to methods intended to predict imminent failure of systems or components, and potentially enable mechanisms to avoid or counteract failure issues, or recommend maintenance of systems prior to failure.
The preservation of optical media is essential because it is a resource in libraries, and stores audio, video, and computer data to be accessed by patrons. While optical discs are generally more reliable and durable than older media types, environmental conditions and/or poor handling can result in lost information.
In digital storage, a Medium Error is a class of errors that a storage device can experience, which imply that a physical problem was encountered when trying to access the device. The word "medium" refers to the physical storage layer, the medium on which the data is stored; as opposed to errors related to e.g. protocol, device/controller/driver state, etc.
High temperature and humidity and fluctuations may cause the magnetic and base layers in a reel of tape to separate, or cause adjacent loops to block together. High temperatures may also weaken the magnetic signal, and ultimately de-magnetise the magnetic layer.
The longevity of magnetic media is most seriously affected by processes that attack the binder resin. Moisture from the air is absorbed by the binder and reacts with the resin. The result is a gummy residue that can deposit on tape heads and cause tape layers to stick together. Reaction with moisture also can result in breaks in the long molecular chains of the binder. This weakens the physical properties of the binder and can result in a lack of adhesion to the backing. These reactions are greatly accelerated by the presence of acids. Typical sources would be the usual pollutant gases in the air, such as sulphur dioxide (SO2) and nitrous oxides (NOx), which react with moist air to form acids. Though acid inhibitors are usually built into the binder layer, over time they can lose their effectiveness.