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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. The phenomenon is also known as data decay, data rot or bit rot.

Visual example

Below are several digital images illustrating data degradation, all consisting of 326,272 bits. The original photo is displayed on the left. In the next image to the right, 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).

In RAM

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[1] or other high-energy particles. Such data degradation is known as a soft error.[2] ECC memory can be used to mitigate this type of data degradation.[citation needed]

In storage

Data degradation results from the gradual decay of storage media over the course of years or longer. Causes vary by medium:

Component and system failures

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.[6]

Low-level disk controllers typically employ error correction codes (ECC) to correct erroneous data.[7]

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.[8] The ZFS file system was designed to address many of these data corruption issues.[9] The Btrfs file system also includes data protection and recovery mechanisms,[10] as does ReFS.[11]

See also

References

  1. ^ "The Invisible Neutron Threat | National Security Science Magazine". Los Alamos National Laboratory. Retrieved 2020-03-13.
  2. ^ O'Gorman, T. J.; Ross, J. M.; Taber, A. H.; Ziegler, J. F.; Muhlfeld, H. P.; Montrose, C. J.; Curtis, H. W.; Walsh, J. L. (January 1996). "Field testing for cosmic ray soft errors in semiconductor memories". IBM Journal of Research and Development. 40 (1): 41–50. doi:10.1147/rd.401.0041.
  3. ^ Riss, Dan (July 1993). "Conserve O Gram (number 19/8) Preservation Of Magnetic Media" (PDF). nps.gov. Harpers Ferry, West Virginia: National Park Service / Department of the Interior (US). p. 2. 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.
  4. ^ "Preserving magnetic media". National Archives of Australia. Retrieved 3 November 2020. 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.
  5. ^ "QPxTool glossary". qpxtool.sourceforge.io. QPxTool. 2008-08-01. Retrieved 22 July 2020.
  6. ^ Gray, Jim; van Ingen, Catharine (December 2005). "Empirical Measurements of Disk Failure Rates and Error Rates" (PDF). Microsoft Research Technical Report MSR-TR-2005-166. Retrieved 4 March 2013.
  7. ^ "ECC and Spare Blocks help to keep Kingston SSD data protected from errors". Kingston Technology Company. Retrieved 30 March 2021.
  8. ^ Salter, Jim (15 January 2014). "Bitrot and atomic COWs: Inside "next-gen" filesystems". Ars Technica. Archived from the original on 6 March 2015. Retrieved 15 January 2014.
  9. ^ Bonwick, Jeff. "ZFS: The Last Word in File Systems" (PDF). Storage Networking Industry Association (SNIA). Archived from the original (PDF) on 21 September 2013. Retrieved 4 March 2013.
  10. ^ "btrfs Wiki: Features". The btrfs Project. Retrieved 19 September 2013.
  11. ^ Wlodarz, Derrick. "Windows Storage Spaces and ReFS: is it time to ditch RAID for good?". Betanews. Retrieved 2014-02-09.