Editing Hard disk drive (section)

=== {{anchor|ERRORRATESHANDLING}}Error rates and handling ===
Modern drives make extensive use of [[error correction code]]s (ECCs), particularly [[Reed–Solomon error correction]]. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity.<ref>{{cite web |url=https://www.karlstechnology.com/blog/hard-drive-error-correcting-code-ecc/ |title=Hard Drive Error Correcting Code (ECC) |publisher=The PC Guide |last=Kozierok |first=Charles |access-date=May 26, 2019 |date=November 25, 2018 |archive-url=https://web.archive.org/web/20190526072642/https://www.karlstechnology.com/blog/hard-drive-error-correcting-code-ecc/ |archive-date=May 26, 2019 |url-status=live }}</ref> For example, a typical 1&nbsp;[[Terabyte|TB]] hard disk with 512-byte sectors provides additional capacity of about 93&nbsp;[[Gibibyte|GB]] for the [[forward error correction|ECC]] data.<ref>{{cite web
 | url = https://www.idema.org/wp-content/uploads/downloads/2011/12/AF-in-Legacy-Infrastructures-SDC2011_IDEMA-AF.pdf
 | title = Advanced Format in Legacy Infrastructures: More Transparent than Disruptive
 | year = 2011
 | access-date = November 5, 2013
 | first = Curtis E.
 | last = Stevens
 | website = idema.org
 | archive-url = https://web.archive.org/web/20131105222506/http://www.idema.org/wp-content/uploads/downloads/2011/12/AF-in-Legacy-Infrastructures-SDC2011_IDEMA-AF.pdf
 | archive-date = November 5, 2013
 | url-status = dead
 }}</ref>

In the newest drives, {{as of|2009|lc=on}},<ref name="AutoMK-21" /> [[low-density parity-check code]]s (LDPC) were supplanting Reed–Solomon; LDPC codes enable performance close to the [[Shannon limit]] and thus provide the highest storage density available.<ref name="AutoMK-21" /><ref>[https://docplayer.net/3699743-2-5-inch-hard-disk-drive-with-high-recording-density-and-high-shock-resistance.html "2.5-inch Hard Disk Drive with High Recording Density and High Shock Resistance] {{Webarchive|url=https://web.archive.org/web/20190526075908/https://docplayer.net/3699743-2-5-inch-hard-disk-drive-with-high-recording-density-and-high-shock-resistance.html |date=May 26, 2019 }}, Toshiba, 2011</ref>

Typical hard disk drives attempt to "remap" the data in a [[Bad sector|physical sector that is failing]] to a spare physical sector provided by the drive's "spare sector pool" (also called "reserve pool"),<ref>{{cite web|author=MjM Data Recovery Ltd |url=http://datarecovery.mjm.co.uk/sectorremapping.html |archive-url=https://web.archive.org/web/20140201174433/http://datarecovery.mjm.co.uk/sectorremapping.html| title=MJM Data Recovery Ltd: Hard Disk Bad Sector Mapping Techniques |website=Datarecovery.mjm.co.uk |access-date=January 21, 2014 | archive-date=February 1, 2014}}</ref> while relying on the ECC to recover stored data while the number of errors in a bad sector is still low enough. The S.M.A.R.T ([[Self-Monitoring, Analysis and Reporting Technology]]) feature counts the total number of errors in the entire HDD fixed by ECC (although not on all hard drives as the related S.M.A.R.T attributes "Hardware ECC Recovered" and "Soft ECC Correction" are not consistently supported), and the total number of performed sector remappings, as the occurrence of many such errors may predict an [[HDD failure]].

The "No-ID Format", developed by IBM in the mid-1990s, contains information about which sectors are bad and where remapped sectors have been located.<ref>{{cite web |url=https://www.karlstechnology.com/blog/hard-drive-sector-format-and-structure/ |title=Hard Drive Sector Format and Structure |publisher=The PC Guide |last=Kozierok |first=Charles |access-date=May 26, 2019 |date=December 23, 2018 |archive-url=https://web.archive.org/web/20190526072622/https://www.karlstechnology.com/blog/hard-drive-sector-format-and-structure/ |archive-date=May 26, 2019 |url-status=live }}</ref>

Only a tiny fraction of the detected errors end up as not correctable. Examples of specified uncorrected bit read error rates include:
* 2013 specifications for enterprise SAS disk drives state the error rate to be one uncorrected bit read error in every 10<sup>16</sup> bits read,<ref name="SGAT2013">{{cite web
 | url = https://www.seagate.com/files/www-content/product-content/savvio-fam/enterprise-performance-15k-hdd/savvio-15k-4/en-us/enterprise-performance-15k-hdd-ds1797-1-1307us.pdf
 | title = Enterprise Performance 15K HDD: Data Sheet
 | year = 2013
 | access-date = October 24, 2013
 | publisher = Seagate
 | archive-url = https://web.archive.org/web/20131029192706/http://www.seagate.com/files/www-content/product-content/savvio-fam/enterprise-performance-15k-hdd/savvio-15k-4/en-us/enterprise-performance-15k-hdd-ds1797-1-1307us.pdf
 | archive-date = October 29, 2013
 | url-status = live
 }}</ref><ref name="WD2013">{{cite web
 | url = https://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771463.pdf
 | title = WD Xe: Datacenter hard drives
 | year = 2013
 | access-date = October 24, 2013
 | publisher = Western Digital
 | archive-url = https://web.archive.org/web/20131029193439/http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771463.pdf
 | archive-date = October 29, 2013
 | url-status = live
 }}</ref> 
* 2018 specifications for consumer SATA hard drives state the error rate to be one uncorrected bit read error in every 10<sup>14</sup> bits.<ref name="SGAT2018">{{cite web
 | title = 3.5" BarraCuda data sheet
 | publisher = Seagate
 | date = June 2018
 | url = https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracudaDS1900-11-1806US-en_US.pdf
 | access-date = July 28, 2018
 | archive-url = https://web.archive.org/web/20180728070449/https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracudaDS1900-11-1806US-en_US.pdf
 | archive-date = July 28, 2018
 | url-status = live
 }}</ref><ref name="WD2018">{{cite web
 | title = WD Red Desktop/Mobile Series Spec Sheet
 | publisher = Western Digital
 | date = April 2018
 | url = https://www.wdc.com/content/dam/wdc/website/downloadable_assets/eng/spec_data_sheet/2879-800002.pdf
 | access-date = July 28, 2018
 | archive-url = https://web.archive.org/web/20180728070730/https://www.wdc.com/content/dam/wdc/website/downloadable_assets/eng/spec_data_sheet/2879-800002.pdf
 | archive-date = July 28, 2018
 | url-status = live
 }}</ref>
Within a given manufacturers model the uncorrected bit error rate is typically the same regardless of capacity of the drive.<ref name="SGAT2013" /><ref name="WD2013" /><ref name="SGAT2018" /><ref name="WD2018" />

The worst type of errors are [[silent data corruption]]s which are errors undetected by the disk firmware or the host operating system; some of these errors may be caused by hard disk drive malfunctions while others originate elsewhere in the connection between the drive and the host.<ref>{{Cite news |title= Keeping Bits Safe: How Hard Can It Be? |work= ACM Queue |date= October 1, 2010 |author= David S. H. Rosenthal |url= https://queue.acm.org/detail.cfm?id=1866298 |access-date= January 2, 2014 |author-link= David S. H. Rosenthal |archive-url= https://web.archive.org/web/20131217020947/http://queue.acm.org/detail.cfm?id=1866298 |archive-date= December 17, 2013 |url-status= live }}</ref>

{{Anchor|TDMR}}