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{{short description|Monitoring system in computer drives}}
{{missing information|article|S.M.A.R.T. on NVM express, with a standardized "Get Log Page" operation|date=November 2019}}

'''S.M.A.R.T.''' ('''Self-Monitoring, Analysis and Reporting Technology'''; often written as '''SMART''') is a monitoring system included in [[Computer|computer]] [[Engineering:Hard disk drive|hard disk drive]]s (HDDs) and [[Solid-state drive|solid-state drive]]s (SSDs).<ref>{{cite web|url=http://www.samsung.com/global/business/semiconductor/minisite/SSD/global/html/about/whitepaper07.html|archive-url=https://web.archive.org/web/20150310051031/http://www.samsung.com/global/business/semiconductor/minisite/SSD/global/html/whitepaper/whitepaper07.html |archive-date=2015-03-10 |url-status=dead |title=Communicating With Your SSD: Understanding SMART Attributes &#124; Samsung SSD |publisher=Samsung.com |access-date=2014-01-18}}</ref> Its primary function is to detect and report various indicators of drive reliability with the intent of  anticipating imminent hardware failures.

When S.M.A.R.T. data indicates a possible imminent drive failure, software running on the host system may notify the user so preventive action can be taken to prevent data loss, and the failing drive can be replaced and data integrity maintained.

== Background ==

Hard disk and other storage drives are subject to failures (see [[Hard disk drive failure|hard disk drive failure]]) which can be classified within two basic classes:

* ''Predictable failures'' which result from slow processes such as mechanical wear and gradual degradation of storage surfaces. Monitoring can determine when such failures are becoming more likely.
* ''Unpredictable failures'' which occur without warning due to anything from electronic components becoming defective to a sudden mechanical failure, including failures related to improper handling.

Mechanical failures account for about 60% of all drive failures.<ref name="seagate1">{{Citation | url = http://www.seagate.com/docs/pdf/whitepaper/enhanced_smart.pdf | publisher = Seagate | type = statement | title = Enhanced Smart attributes | url-status = dead | archive-url = https://web.archive.org/web/20060328023033/http://seagate.com/docs/pdf/whitepaper/enhanced_smart.pdf | archive-date = 2006-03-28 }}</ref>
While the eventual failure may be catastrophic, most mechanical failures result from gradual wear and there are usually certain indications that failure is imminent. These may include increased heat output, increased noise level, problems with reading and writing of data, or an increase in the number of damaged disk sectors.

PCTechGuide's page on S.M.A.R.T. (2003) comments that the technology has gone through three phases:<ref name="PCTechGuide">{{Citation|title=SMART|url=https://www.pctechguide.com/hard-disks/hard-disk-smart-drives|year=2003|publisher=PCTechGuide}}</ref>
{{Quote | In its original incarnation S.M.A.R.T. provided failure prediction by monitoring certain online hard drive activities.
A subsequent version of the standard improved failure prediction by adding an automatic off-line read scan to monitor additional operations. online attributes are always updated while the offline attributes get updated when the HDD is not under working condition. If there is an immediate need to update the offline attributes, the HDD slows down and the offline attributes get updated. The latest "S.M.A.R.T." technology not only monitors hard drive activities but adds failure prevention by attempting to detect and repair sector errors. 
Also, while earlier versions of the technology only monitored hard drive activity for data that was retrieved by the operating system, this latest S.M.A.R.T. tests all data and all sectors of a drive by using "off-line data collection" to confirm the drive's health during periods of inactivity.}}

===Accuracy===
A field study at [[Company:Google|Google]]<ref name=":0">{{Cite web | url=https://ai.google/research/pubs/pub32774 |title = Failure Trends in a Large Disk Drive Population|year = 2007| pages=17–29 }}</ref> covering over 100,000 consumer-grade drives from December 2005 to August 2006 found correlations between certain S.M.A.R.T. information and annualized failure rates:
* In the 60 days following the first uncorrectable error on a drive (S.M.A.R.T. attribute 0xC6 or 198) detected as a result of an offline scan, the drive was, on average, 39 times more likely to fail than a similar drive for which no such error occurred.
* First errors in reallocations, offline reallocations (S.M.A.R.T. attributes 0xC4 and 0x05 or 196 and 5) and probational counts (S.M.A.R.T. attribute 0xC5 or 197) were also strongly correlated to higher probabilities of failure. 
* Conversely, little correlation was found for increased temperature and no correlation for usage level.  However, the research showed that a large proportion (56%) of the failed drives failed without recording any count in the "four strong S.M.A.R.T. warnings" identified as scan errors, reallocation count, offline reallocation and probational count. 
* Further, 36% of failed drives did so without recording any S.M.A.R.T. error at all, except the temperature, meaning that S.M.A.R.T. data alone was of limited usefulness in anticipating failures.<ref name="research.google.com">{{Citation | url = http://research.google.com/archive/disk_failures.pdf | title = Failure Trends in a Large Disk Drive Population | chapter = Conclusion | first1 = Eduardo | last1 = Pinheiro | first2 = Wolf-Dietrich | last2 = Weber | first3 = Luís André | last3 = Barroso | location = Mountain View, CA}}</ref>

== History and predecessors ==
An early hard disk monitoring technology was introduced by [[Company:IBM|IBM]] in 1992 in its IBM 9337 Disk Arrays for AS/400 servers using IBM 0662 SCSI-2 disk drives.<ref>{{Citation | url = http://www-306.ibm.com/common/ssi/OIX.wss?DocURL=http://d03xhttpcl001g.boulder.ibm.com/common/ssi/rep_ca/9/877/ENUSZG92-0289/index.html&InfoType=AN | publisher = IBM | type = announcement letter | title = No. ZG92-0289 | date = September 1, 1992}}</ref> Later it was named Predictive Failure Analysis (PFA) technology. It was measuring several key device health parameters and evaluating them within the drive firmware.  Communications between the physical unit and the monitoring software were limited to a binary result: namely, either "device is OK" or "drive is likely to fail soon".

Later, another variant, which was named IntelliSafe, was created by computer manufacturer [[Company:Compaq|Compaq]] and disk drive manufacturers [[Company:Seagate Technology|Seagate]], Quantum, and Conner.<ref>{{Citation | title = Playing it S.M.A.R.T.: The emergence of reliability prediction technology. | type = technical report | publisher = Seagate Technology Paper | first1=Eric | last1=Ottem | first2=Judy | last2=Plummer | date=1995}}</ref>  The disk drives would measure the disk's "health parameters", and the values would be transferred to the operating system and user-space monitoring software. Each disk drive vendor was free to decide which parameters were to be included for monitoring, and what their thresholds should be. The unification was at the protocol level with the host.

Compaq submitted IntelliSafe to the Small Form Factor (SFF) committee for standardization in early 1995.<ref>{{Citation | title = Compaq. IntelliSafe. Technical Report SSF-8035 | publisher = Small Form Committee |date=January 1995}}</ref> It was supported by IBM, by Compaq's development partners Seagate, Quantum, and Conner, and by [[Company:Western Digital|Western Digital]], which did not have a failure prediction system at the time. The Committee chose IntelliSafe's approach, as it provided more flexibility.  Compaq placed IntelliSafe into the public domain on 12 May 1995.<ref>{{cite report|author1=Seagate Product Marketing|title=Get S.M.A.R.T. for Reliability|date=July 1999|archive-date=12 June 2001|archive-url=https://web.archive.org/web/20010612122823/http://www.seagate.com/newsinfo/docs/disc/enhanced_smart.pdf|url=http://www.seagate.com/newsinfo/docs/disc/enhanced_smart.pdf|series=Technology Paper|publisher=Seagate Technology|location=Scotts Valley, California|language=en|id=TP-67D|quote=Compaq placed IntelliSafe in the public domain by presenting its specification for the ATA environment, SFF-8035, to the Small Form Factor Committee on May 12, 1995.}}</ref>  The resulting jointly developed standard was named S.M.A.R.T..

That SFF standard described a communication protocol for an ATA host to use and control monitoring and analysis in a hard disk drive, but did not specify any particular metrics or analysis methods.  Later, "S.M.A.R.T." came to be understood (though without any formal specification) to refer to a variety of specific metrics and methods and to apply to protocols unrelated to ATA for communicating the same kinds of things.

== Provided information ==
[[File:Intel 525 mSATA SSD.jpg|thumb|mSATA SSD with SandForce SF-2281 Controller (Intel 525 mSATA SSD)]]
The technical documentation for S.M.A.R.T. is in the AT Attachment (ATA) standard. First introduced in 1994,<ref>{{Cite book|last=Mueller|first=Scott|url=https://www.worldcat.org/oclc/816159579|title=Upgrading and repairing PCs|date=2013|isbn=978-0-7897-5000-6|edition=21st|location=Indianapolis, Ind.|chapter=The ATA/IDE Interface|oclc=816159579|chapter-url=https://www.informit.com/articles/article.aspx?p=2028834&seqNum=2}}</ref> the ATA standard has gone through multiple revisions. Some parts of the original S.M.A.R.T. specification by the [[Organization:Small Form Factor Committee|Small Form Factor (SFF) Committee]] were added to ATA-3,<ref name=":6">{{Cite web|last=Allen|first=Bruce|date=2004-01-01|title=Monitoring Hard Disks with SMART {{!}} Linux Journal|url=https://www.linuxjournal.com/article/6983|access-date=2021-04-13|website=www.linuxjournal.com}}</ref> published in 1997. In 1998 ATA-4 dropped the requirement for drives to maintain an internal attribute table and instead required only for an "OK" or "NOT OK" value to be returned.<ref name=":6" /> Albeit, manufacturers have kept the capability to retrieve the attributes' value. The most recent ATA standard, ATA-8, was published in 2004.<ref name="D1699r0">{{Citation|title=AT Attachment 8 – ATA/ATAPI Command Set (ATA8-ACS)|type=working draft|publisher=ANSI INCITS|date=September 6, 2008|chapter-url= http://www.t13.org/documents/uploadeddocuments/docs2008/d1699r6a-ata8-acs.pdf|chapter=Section 4.8: "SMART (Self-monitoring, analysis, and reporting technology) feature set"}}</ref> It has undergone regular revisions,<ref name="D1699r3f">{{Harvnb | Stephens | 2006 | pp =44–126, 198–213, 327–44 | loc = Sections 4.19: "SMART (Self-monitoring, analysis, and reporting technology) feature set", 7.52: "SMART", Annex A: "Log Page Definitions"}}</ref> the latest being in 2011.<ref name="ACS-2">{{Citation | work= ATA Command Set 2 | title = ATA/ATAPI Command Set - 2 (ACS-2) | type = working draft | edition = 7 |publisher= ANSI INCITS |date = June 22, 2011 | url = http://www.t13.org/documents/UploadedDocuments/docs2011/d2015r7-ATAATAPI_Command_Set_-_2_ACS-2.pdf}}</ref> Standardization of similar features on SCSI is more scarce and is not named as such on standards, although vendors and consumers alike do refer to these similar features at S.M.A.R.T. too.<ref>{{cite web |last1=Gilbert |first1=Douglas |title=Smartmontools for SCSI devices |url=https://www.smartmontools.org/browser/trunk/www/smartmontools_scsi.xml}}</ref>

The most basic information that S.M.A.R.T. provides is the S.M.A.R.T. status. It provides only two values: "threshold not exceeded" and "threshold exceeded". Often these are represented as "drive OK" or "drive fail" respectively. A "threshold exceeded" value is intended to indicate that there is a relatively high probability that the drive will not be able to honor its specification in the future: that is, the drive is "about to fail". The predicted failure may be catastrophic or may be something as subtle as the inability to write to certain sectors, or perhaps slower performance than the manufacturer's declared minimum.

The S.M.A.R.T. status does not necessarily indicate the drive's past or present reliability. If a drive has already failed catastrophically, the S.M.A.R.T. status may be inaccessible. Alternatively, if a drive has experienced problems in the past, but the sensors no longer detect such problems, the S.M.A.R.T. status may, depending on the manufacturer's programming, suggest that the drive is now healthy.

The inability to ''read'' some sectors is not always an indication that a drive is about to fail. One way that unreadable sectors may be created, even when the drive is functioning within specification, is through a sudden power failure while the drive is writing.  Also, even if the physical disk is damaged at one location, such that a certain sector is unreadable, the disk may be able to use spare space to replace the bad area, so that the sector can be overwritten.<ref>{{Citation | publisher = Hitachi Data Systems | date = 19 September 2003 | type = hard disk drive specification | title = Hitachi Travelstar 80GN | edition = 2.0 | id = Hitachi Document Part Number S13K-1055-20 | url = http://www.hitachigst.com/tech/techlib.nsf/techdocs/85CC1FF9F3F11FE187256C4F0052E6B6/$file/80GNSpec2.0.pdf | url-status = dead | archive-url = https://web.archive.org/web/20110718181944/http://www.hitachigst.com/tech/techlib.nsf/techdocs/85CC1FF9F3F11FE187256C4F0052E6B6/$file/80GNSpec2.0.pdf | archive-date = 18 July 2011 }}</ref>

More detail on the health of the drive may be obtained by examining the S.M.A.R.T. Attributes. S.M.A.R.T. Attributes were included in some drafts of the ATA standard, but were removed before the standard became final. The meaning and interpretation of the attributes varies between manufacturers, and are sometimes considered a trade secret for one manufacturer or another. Attributes are further discussed below.<ref name=hatfield2005 />

Drives with S.M.A.R.T. may optionally maintain a number of 'logs'. The ''error log'' records information about the most recent errors that the drive has reported back to the host computer. Examining this log may help one to determine whether computer problems are disk-related or caused by something else (error log timestamps may "wrap" after 2<sup>32</sup> [[Millisecond|ms]] = 49.71 days<ref>{{Citation | url = http://smartmontools.sourceforge.net/examples/MAXTOR-1.txt | publisher = Source forge | title = Smartmontools | contribution = Maxtor | format = plain text | type = example}}</ref>)

A drive that implements S.M.A.R.T. may optionally implement a number of self-test or maintenance routines, and the results of the tests are kept in the ''self-test log''. The self-test routines may be used to detect any unreadable sectors on the disk, so that they may be restored from back-up sources (for example, from other disks in a RAID). This helps to reduce the risk of incurring permanent loss of data.

== Standards and implementation ==

===Lack of common interpretation===
Many motherboards display a warning message when a disk drive is approaching failure. Although an industry standard exists among most major hard drive manufacturers,<ref name=PCTechGuide /> issues remain due to attributes intentionally left undocumented to the public in order to differentiate models between manufacturers.<ref>{{cite web|author1=Bruno Sonnino|title=What is S.M.A.R.T.?|url=https://www.pcmag.com/article2/0,2817,1879485,00.asp|website=PC Mag|publisher=Ziff Davis|access-date=12 July 2016|pages=1|language=en|date=31 October 2005}}</ref><ref name=hatfield2005>{{cite web|last = Hatfield | first = Jim |title=SMART Attribute Annex|url=http://www.t13.org/documents/uploadeddocuments/docs2005/e05148r0-acs-smartattributesannex.pdf|website=Technical Committee T13|publisher=Seagate Technology|access-date=12 July 2016|pages=1–5|language=en|date=30 September 2005| id = e05148r0}}</ref>
From a legal perspective, the term "S.M.A.R.T." refers only to a signaling method between internal disk drive electromechanical sensors and the host computer. Because of this the specifications of S.M.A.R.T. are entirely vendor specific and, while many of these attributes have been standardized between drive vendors, others remain vendor-specific. S.M.A.R.T. implementations still differ and in some cases may lack "common" or expected features such as a temperature sensor or only include a few select attributes while still allowing the manufacturer to advertise the product as "S.M.A.R.T. compatible."<ref name=hatfield2005 />

===Visibility to host systems===
Depending on the type of interface being used, some S.M.A.R.T.-enabled motherboards and related software may not communicate with certain S.M.A.R.T.-capable drives. For example, few external drives connected via USB and FireWire correctly send S.M.A.R.T. data over those interfaces. With so many ways to connect a hard drive ([[Engineering:SCSI|SCSI]], [[Engineering:Fibre Channel|Fibre Channel]], ATA, [[Engineering:Serial ATA|SATA]], [[Engineering:Serial Attached SCSI|SAS]], [[Serial Storage Architecture|SSA]], [[Engineering:NVM Express|NVMe]] and so on), it is difficult to predict whether S.M.A.R.T. reports will function correctly in a given system.

Even with a hard drive and interface that implements the specification, the computer's operating system may not see the S.M.A.R.T. information because the drive and interface are encapsulated in a lower layer.  For example, they may be part of a RAID subsystem in which the RAID controller sees the S.M.A.R.T.-capable drive, but the host computer sees only a logical volume generated by the RAID controller.

On the [[Software:Microsoft Windows|Windows]] platform, many programs designed to monitor and report S.M.A.R.T. information will function only under an administrator account.

[[BIOS]] and [[Software:Windows|Windows]] ([[Software:Windows Vista|Windows Vista]] and later) may detect S.M.A.R.T. status of hard disk drives and solid state drives, and prompt if S.M.A.R.T. status bad.<ref>{{Cite web|date=2019-08-27|title=Hard drive acting up? It could be hardware issues — here's how to find out|url=https://www.windowscentral.com/how-check-if-hard-drive-failing-smart-windows-10|access-date=2021-03-04|website=Windows Central}}</ref>

== Access ==
For a list of various programs that allow reading of S.M.A.R.T. Data, see [[Engineering:Comparison of S.M.A.R.T. tools|Comparison of S.M.A.R.T. tools]].

== ATA S.M.A.R.T. attributes ==
Each drive manufacturer defines a set of attributes,{{Sfn | Stephens | 2006 | p = 207 | ps = Of the 512 octets listed in table 42 on page 207: "Device SMART data structure" a total of 489 are marked as "Vendor specific".}}<ref>{{Citation | title = Playing it S.M.A.R.T.: The emergence of reliability prediction technology. | type = technical report | publisher = Seagate Technology Paper | first1=Eric | last1=Ottem | first2=Judy | last2=Plummer | date=1995 | quote=Though attributes are drive-specific, a variety of typical characteristics can be identified: [...] The attributes listed above illustrate typical kinds of reliability indicators. Ultimately, the disc drive design determines which attributes the manufacturer will choose. Attributes are therefore considered proprietary, since they depend on drive design.}}</ref> and sets threshold values beyond which attributes should not pass under normal operation.  Each attribute has a ''raw value'' that can be a decimal or a hexadecimal value, whose meaning is entirely up to the drive manufacturer (but often corresponds to counts or a physical unit, such as degrees Celsius or seconds), a ''normalized value'', which ranges from 1 to 253 (with 1 representing the worst case and 253 representing the best) and a ''worst value'', which represents the lowest recorded normalized value. The initial default value of attributes is 100 but can vary between manufacturer.<ref name=hatfield2005 />

Manufacturers that have implemented at least one S.M.A.R.T. attribute in various products include [[Company:Samsung Electronics|Samsung]], [[Company:Seagate Technology|Seagate]], [[Company:IBM|IBM]] (Hitachi), [[Company:Fujitsu|Fujitsu]], Maxtor, [[Company:Toshiba|Toshiba]], [[Company:Intel|Intel]], [[Company:STec, Inc.|sTec, Inc.]], [[Company:Western Digital|Western Digital]] and [[Company:ExcelStor Technology|ExcelStor Technology]].

=== Known ATA S.M.A.R.T. attributes ===

The following chart lists some S.M.A.R.T. attributes and the typical meaning of their raw values. Normalized values are usually mapped so that higher values are better (exceptions include drive temperature, number of head load/unload cycles<ref>{{Citation | publisher = Source forge | url = https://www.smartmontools.org/wiki/FAQ#Attribute194TemperatureCelsiusbehavesstrangelyonmySeagatedisk | title = Smartmontools | contribution = FAQ | quote = Attribute 194 (Temperature Celsius) behaves strangely on my Seagate disk}}</ref>), but higher ''raw'' attribute values may be better or worse depending on the attribute and manufacturer. For example, the "Reallocated Sectors Count" attribute's normalized value ''decreases'' as the count of reallocated sectors ''increases''.  In this case, the attribute's ''raw'' value will often indicate the actual count of sectors that were reallocated, although vendors are in no way required to adhere to this convention.

As manufacturers do not necessarily agree on precise attribute definitions and measurement units, the following list of attributes is a general guide only.

Drives do not support all attribute codes (sometimes abbreviated as "ID", for "identifier", in tables). Some codes are specific to particular drive types (magnetic platter, flash, SSD). Drives may use different codes for the same parameter, e.g., see codes 193 and 225.

{| class="wikitable" style="margin:auto; text-align:center;"
|+ Legend
|-
! scope="row" | ID 
  |193<br />0xC1||Attribute code in decimal and<br />hexadecimal notations
|-
! scope="row" rowspan="2" | Ideal
  |[[Image:Dark Green Arrow Up.svg|18px|center|alt=Higher]]{{Center|High}}||Higher raw value is better
  |-
  |{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]||Lower raw value is better
|- style="background:#FED;" 
! scope="row" | !<br />(Critical)
  | [[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
  |Denotes a ''Critical'' attribute.<br />Specific values may predict drive failure
|}

{| class="wikitable sortable" summary="Overview of known S.M.A.R.T. attributes and their description"
|-
! ID ||  Attribute name || Ideal || ! || Description
|- 
| 01<br />0x01 || style="white-space: nowrap;" | '''Read Error Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| (Vendor specific raw value.)  Stores data related to the rate of hardware read errors that occurred when reading data from a disk surface.  The raw value has different structure for different vendors and is often not meaningful as a decimal number. For some drives, this number may increase during normal operation without necessarily signifying errors.
|-
| 02<br />0x02 || '''Throughput Performance''' ||[[Image:Dark Green Arrow Up.svg|18px|center|alt=Higher]]{{Center|High}}
||| Overall (general) throughput performance of a hard disk drive. If the value of this attribute is decreasing there is a high probability that there is a problem with the disk.
|-
| 03<br />0x03 || '''Spin-Up Time''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Average time of spindle spin up (from zero RPM to fully operational [milliseconds]).
|-
| 04<br />0x04 || '''Start/Stop Count''' || 
||| A tally of spindle start/stop cycles. The spindle turns on, and hence the count is increased, both when the hard disk is turned on after having before been turned entirely off (disconnected from power source) and when the hard disk returns from having previously been put to sleep mode.<ref>{{Citation | date=2009-03-10 | title= Smart Linux | publisher = Source forge | contribution = Self-Monitoring, Analysis and Reporting Technology (SMART) | type = article | url = http://smartlinux.sourceforge.net/smart/article.php}}</ref>
|- style="background:#FED;"
| 05<br />0x05 || '''Reallocated Sectors Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":1">{{Cite journal|year=2007|title=Failure Trends in a Large Disk Drive Population|url=https://static.googleusercontent.com/media/research.google.com/en//archive/disk_failures.pdf|journal=Proceedings of the 5th USENIX Conference on File and Storage Technologies (FAST'07)|quote=We find that the group of drives with scan errors are ten times more likely to fail than the group with no errors. This effect is also noticed when we further break down the groups by disk model. From Figure 8 we see a drastic and quick decrease in survival probability after the first scan error (left graph). A little over 70% of the drives survive the first 8 months after their first scan error.}}</ref><ref>{{Cite news|url=https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/|title=What SMART Hard Disk Errors Actually Tell Us|date=2016-10-06|work=Backblaze Blog {{!}} Cloud Storage & Cloud Backup|access-date=2017-03-19|language=en-US}}</ref><ref>{{Cite web|url=https://kb.acronis.com/content/9105|title=S.M.A.R.T. Attribute: Reallocated Sectors Count {{!}} Knowledge Base|website=kb.acronis.com|language=en|access-date=2017-03-19}}</ref>}}
| Count of reallocated sectors. The raw value represents a count of the [[Engineering:Bad sector|bad sector]]s that have been found and remapped.<ref>{{Cite web|url=http://www.t13.org/Documents/UploadedDocuments/docs2016/di529r14-ATAATAPI_Command_Set_-_4.pdf|title=ATA Command Set 4 (ACS-4) - Working Draft|date=October 14, 2016}}</ref> Thus, the higher the attribute value, the more sectors the drive has had to reallocate. This value is primarily used as a metric of the life expectancy of the drive; a drive which has had any reallocations at all is significantly more likely to fail in the immediate months.<ref name=":1" /><ref>{{Cite web|url=https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/#comment-2938093635|title=What SMART Stats Tell Us About Hard Drives|date=2016-10-06|at=Comment by "Mark"|quote=There was a direct link between Reallocated Sectors Count and how quickly the drive would fail [...] Even one Uncorrectable sector count would lead to most drives being unusable within 3months}}</ref>
|-
| 06<br />0x06 || '''Read Channel Margin''' || 
||| Margin of a channel while reading data. The function of this attribute is not specified.
|-
| 07<br />0x07 || '''Seek Error Rate''' || {{varies}} 
||| (Vendor specific raw value.) Rate of seek errors of the magnetic heads. If there is a partial failure in the mechanical positioning system, then seek errors will arise. Such a failure may be due to numerous factors, such as damage to a servo, or thermal widening of the hard disk.  The raw value has different structure for different vendors and is often not meaningful as a decimal number. For some drives, this number may increase during normal operation without necessarily signifying errors.
|-
| 08<br />0x08 || '''Seek Time Performance ''' ||[[Image:Dark Green Arrow Up.svg|18px|center|alt=Higher]]{{Center|High}}
||| Average performance of seek operations of the magnetic heads. If this attribute is decreasing, it is a sign of problems in the mechanical subsystem.
|-
| 09<br />0x09 || style="white-space: nowrap;" | '''Power-On Hours''' || 
||| Count of hours in power-on state. The raw value of this attribute shows total count of hours (or minutes, or seconds, depending on manufacturer) in power-on state.<ref>
{{Citation | publisher = Acronis | title = Knowledge Base | contribution = 9109: S.M.A.R.T. Attribute: Power-On Hours (POH) | url = http://kb.acronis.com/content/9109}}</ref>

"By default, the total expected lifetime of a hard disk in perfect condition is defined as 5 years (running every day and night on all days). This is equal to 1825 days in 24/7 mode or 43800 hours."<ref>{{cite web |url=http://www.hdsentinel.com/help/en/54_pot.html |title=Power on time |website=hdsentinel.com |access-date=2014-07-14}}</ref>

On some pre-2005 drives, this raw value may advance erratically and/or "wrap around" (reset to zero periodically).<ref>{{cite web|url= http://sourceforge.net/apps/trac/smartmontools/wiki/FAQ#Thepower-ontimerAttribute9rawvalueonmyMaxtordiskactsstrange |title=FAQ | work = Smartmontools |publisher=Sourceforge | access-date =2013-01-15}}</ref>
|- style="background:#FED;"
| 10<br />0x0A || '''Spin Retry Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref>{{Cite web|url=https://kb.acronis.com/content/9110|title=S.M.A.R.T. Attribute: Spin Retry Count Knowledge Base|website=kb.acronis.com|language=en|access-date=2017-03-19}}</ref>}}
| Count of retry of spin start attempts. This attribute stores a total count of the spin start attempts to reach the fully operational speed (under the condition that the first attempt was unsuccessful). An increase of this attribute value is a sign of problems in the hard disk mechanical subsystem.
|-
| 11<br />0x0B || '''Recalibration Retries''' or '''Calibration Retry Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center| alt=Lower]]
||| This attribute indicates the count that recalibration was requested (under the condition that the first attempt was unsuccessful). An increase of this attribute value is a sign of problems in the hard disk mechanical subsystem.
|-
| 12<br />0x0C || '''Power Cycle Count''' || 
||| This attribute indicates the count of full hard disk power on/off cycles.
|-
| 13<br />0x0D || style="white-space: nowrap;" | '''Soft Read Error Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Uncorrected read errors reported to the operating system.
|-
| 22<br />0x16 || '''Current Helium Level''' ||[[Image:Dark Green Arrow Up.svg|18px|center|alt=Higher]]{{Center|High}}
||| Specific to He8 drives from HGST. This value measures the helium inside of the drive specific to this manufacturer. It is a pre-fail attribute that trips once the drive detects that the internal environment is out of specification.<ref>{{cite web|url=https://www.backblaze.com/blog/smart-22-is-a-gas-gas-gas/|title=SMART Hard Drive Attributes: SMART 22 is a Gas Gas Gas|work=Backblaze Blog - The Life of a Cloud Backup Company|date=2015-04-16}}</ref>
|-
| 23<br />0x17 || '''Helium Condition Lower''' ||
||| Specific to MG07+ drives from Toshiba. This value measures lower level of helium inside of the drive specific to this manufacturer. It is a pre-fail attribute that trips once the drive detects that the internal environment is out of specification.<ref name="Q2 2018">{{cite web|url=https://www.onlinebackupcodes.com/2018/08/27/hard-drive-stats-for-q2-2018/|title=Hard Drive Stats for Q2 2018|work=Backblaze Blog - The Life of a Cloud Backup Company|date=2018-08-27|accessdate=2022-08-07}}</ref>
|-
| 24<br />0x18 || '''Helium Condition Upper''' ||
||| Specific to MG07+ drives from Toshiba. This value measures the upper level helium inside of the drive specific to this manufacturer. It is a pre-fail attribute that trips once the drive detects that the internal environment is out of specification.<ref name="Q2 2018"/>
|-
| 170<br />0xAA || '''Available Reserved Space''' || 
||| See attribute E8.<ref>{{Citation | publisher = Intel | date = March 2014 | title = Intel Solid-state Drive DC S3700 Series Product Specification | type = product manual | number = 32817–007 | url = http://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/ssd-dc-s3700-spec.pdf}}</ref>
|-
| 171<br />0xAB || '''SSD Program Fail Count''' || 
||| (Kingston) The total number of flash program operation failures since the drive was deployed.<ref name=acronis/> Identical to attribute 181.
|-
| 172<br />0xAC || '''SSD Erase Fail Count''' || 
||| (Kingston) Counts the number of flash erase failures. This attribute returns the total number of Flash erase operation failures since the drive was deployed. This attribute is identical to attribute 182. 
|-
| 173<br />0xAD || '''SSD Wear Leveling Count''' || 
||| Counts the maximum worst erase count on any block. 
|-
| 174<br />0xAE || '''Unexpected Power Loss Count''' || 
||| Also known as "Power-off Retract Count" per conventional HDD terminology. Raw value reports the number of unclean shutdowns, cumulative over the life of an SSD, where an "unclean shutdown" is the removal of power without STANDBY IMMEDIATE as the last command (regardless of PLI activity using capacitor power). Normalized value is always 100.<ref name="Intel">{{Citation | publisher = Intel | date = March 2014| title = Intel Solid-state Drive DC S3700 Series Product Specification | type = product manual | number = 32817–007 | url = http://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/ssd-dc-s3700-spec.pdf}}</ref>
|-
| 175<br />0xAF || '''Power Loss Protection Failure''' || 
||| Last test result as microseconds to discharge cap, saturated at its maximum value. Also logs minutes since last test and lifetime number of tests. Raw value contains the following data:
* Bytes 0-1: Last test result as microseconds to discharge cap, saturates at max value. Test result expected in range 25 <= result <= 5000000, lower indicates specific error code.
* Bytes 2-3: Minutes since last test, saturates at max value.
* Bytes 4-5: Lifetime number of tests, not incremented on power cycle, saturates at max value.

Normalized value is set to one on test failure or 11 if the capacitor has been tested in an excessive temperature condition, otherwise 100.<ref name="Intel"/>
|-
|176<br />0xB0 || style="white-space: nowrap;" | '''Erase Fail Count'''
|
|
|S.M.A.R.T. parameter indicates a number of flash erase command failures.<ref>{{Cite web|url = https://kb.acronis.com/content/9184|title = 9184: S.M.A.R.T. Attribute: Erase Fail Count (chip)|date = March 9, 2010}}</ref>
|-
| 177<br />0xB1 || '''Wear Range Delta''' || 
||| Delta between most-worn and least-worn Flash blocks. It describes how good/bad the wearleveling of the SSD works on a more technical way. 
|-
| 178<br />0xB2 || '''Used Reserved Block Count'''<!-- (Used_Rsvd_Blk_Cnt) --> || 
||| "Pre-Fail" attribute used at least in Samsung devices.
|-
| 179<br />0xB3 || '''Used Reserved Block Count Total'''<!-- (Used_Rsvd_Blk_Cnt_Tot) --> || 
||| "Pre-Fail" attribute used at least in Samsung devices.<ref name="Samsung">{{Citation | publisher = Samsung | date = March 2019 | title = Over-Provisioning Benefits for Samsung Data Center SSDs | type = white paper | url = https://www.samsung.com/semiconductor/global.semi.static/S190311-SAMSUNG-Memory-Over-Provisioning-White-paper.pdf}}</ref>
|-
| 180<br />0xB4 || '''Unused Reserved Block Count Total'''<!-- (Unused_Rsvd_Blk_Cnt_Tot) --> || 
||| "Pre-Fail" attribute used at least in HP devices.
|-
| 181<br />0xB5 || '''Program Fail Count Total''' or '''Non-4K Aligned Access Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Total number of Flash program operation failures since the drive was deployed.<ref>{{cite web|title=SMART Attribute Details|url=http://media.kingston.com/support/downloads/MKP_306_SMART_attribute.pdf|publisher=Kingston Technology Corporation|access-date=3 August 2013|archive-url=https://web.archive.org/web/20130507072056/http://media.kingston.com/support/downloads/MKP_306_SMART_attribute.pdf|archive-date=2013-05-07|page=4|year=2013}}</ref><br /> Number of user data accesses (both reads and writes) where LBAs are not 4 KiB aligned (LBA % 8 != 0) or where size is not modulus 4 KiB (block count != 8), assuming logical block size (LBS) = 512 B.<ref>{{cite web|title=The SMART Command Feature Set|url=http://www.micron.com/~/media/Documents/Products/Technical%20Note/Solid%20State%20Storage/tnfd03.pdf|publisher=Micron Technology, Inc|access-date=3 August 2013|archive-url=https://web.archive.org/web/20130201025337/http://www.micron.com/~/media/Documents/Products/Technical%20Note/Solid%20State%20Storage/tnfd03.pdf|archive-date=2013-02-01|page=11|date=August 2010}}</ref> 
|-
| 182<br />0xB6 || '''Erase Fail Count''' || 
||| "Pre-Fail" Attribute used at least in Samsung devices.
|- 
| 183<br />0xB7 || '''SATA Downshift Error Count''' or '''Runtime Bad Block''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Western Digital, Samsung or Seagate attribute: Either the number of downshifts of link speed (e.g. from 6Gbit/s to 3Gbit/s) or the total number of data blocks with detected, uncorrectable errors encountered during normal operation.<ref>{{cite web|url=https://hddguardian.codeplex.com/wikipage?title=STEC|title=HDD Guardian|work=CodePlex|access-date=21 January 2015}}</ref> Although degradation of this parameter can be an indicator of drive aging and/or potential electromechanical problems, it does not directly indicate imminent drive failure.<ref>{{Cite web|url=https://kb.acronis.com/content/9118|title=S.M.A.R.T. Attribute: SATA Downshift Error Count {{!}} Knowledge Base|website=kb.acronis.com|language=en|access-date=2017-03-19}}</ref>
|- style="background:#FED;"
| 184<br />0xB8 || ''' End-to-End error / IOEDC ''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":2">{{Cite web|url=https://kb.acronis.com/content/9264|title=Acronis Drive Monitor: Disk Health Calculation Knowledge Base|website=kb.acronis.com|language=en|access-date=2017-03-19}}</ref>}}
| This attribute is a part of [[Company:Hewlett-Packard|Hewlett-Packard]]'s SMART IV technology, as well as part of other vendors' IO Error Detection and Correction schemas, and it contains a count of parity errors which occur in the data path to the media via the drive's cache RAM.<ref name= HPSMARTIV>{{cite web|title= SMART IV Technology on HP Business Desktop Hard Drives| url= http://h10032.www1.hp.com/ctg/Manual/c01159621.pdf|publisher=Hewlett-Packard|access-date=20 August 2021}}</ref>
|-
| 185<br />0xB9 || '''Head Stability''' || 
||| Western Digital attribute.
|-
| 186<br />0xBA || '''Induced Op-Vibration Detection''' || 
||| Western Digital attribute.
|- style="background:#FED;"
| 187<br />0xBB || '''Reported Uncorrectable Errors''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":3" />}}
| The count of errors that could not be recovered using hardware ECC (see attribute 195).<ref name=":3">{{cite web|url=https://www.backblaze.com/blog/hard-drive-smart-stats/|title=BackBlaze SMART blog|date=12 November 2014 |access-date=20 July 2015}}</ref>
|- style="background:#FED;"
| 188<br />0xBC || '''Command Timeout''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":4">{{Cite news|url=https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/#comment-2938093635|title=What SMART Hard Disk Errors Actually Tell Us|date=2016-10-06|work=Backblaze Blog {{!}} Cloud Storage & Cloud Backup|access-date=2017-03-19|language=en-US}}</ref>}}
| The count of aborted operations due to HDD timeout.  Normally this attribute value should be equal to zero.<ref name=":4" />
|-
| 189<br />0xBD ||  '''High Fly Writes''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| HDD manufacturers implement a [[Flying height|flying height]] sensor that attempts to provide additional protections for write operations by detecting when a recording head is flying outside its normal operating range. If an unsafe fly height condition is encountered, the write process is stopped, and the information is rewritten or reallocated to a safe region of the hard drive. This attribute indicates the count of these errors detected over the lifetime of the drive.
This feature is implemented in most modern Seagate drives<ref name="seagate1"/>
and some of Western Digital's drives, beginning with the WD Enterprise WDE18300 and WDE9180 Ultra2 SCSI hard drives, and will be included on all future WD Enterprise products.<ref>{{Citation | publisher = Western Digital | date =April 1999 | title=Fly Height Monitor Improves Hard Drive Reliability | id = 79-850123-000 | url =http://www.wdc.com/wdproducts/library/other/2579-850123.pdf}}</ref>
|-
| 190<br />0xBE ||  '''Temperature Difference''' or '''Airflow Temperature''' ||{{varies}} 
||| Value is equal to (100-temp. °C), allowing manufacturer to set a minimum threshold which corresponds to a maximum temperature. This also follows the convention of 100 being a best-case value and lower values being undesirable. However, some older drives may instead report raw Temperature (identical to 0xC2) or Temperature minus 50 here.
|-
| 191<br />0xBF || style="white-space: nowrap;" | '''G-sense Error Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The count of errors resulting from externally induced shock and vibration.
|-
| 192<br />0xC0 ||  '''Power-off Retract Count''', '''Emergency Retract Cycle Count''' (Fujitsu),<ref name="Fujitsu MHT20xxAT">{{Citation | publisher=Fujitsu | date=2003-07-04 | title= MHT2080AT, MHT2060AT, MHT2040AT, MHT2030AT, MHG2020AT Disk Drives | type = product manual | id=C141-E192-02EN | url = http://www.fujitsu.com/downloads/COMP/fcpa/hdd/discontinued/mht20xxat_prod-manual.pdf }}</ref> or '''Unsafe Shutdown Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Number of power-off or emergency retract cycles.<ref name=hatfield2005 /><ref name=acroniskb>{{cite web|title=9127: S.M.A.R.T. Attribute: Power-off Retract Count|url=https://kb.acronis.com/content/9127|website=Acronis Knowledge Base|publisher=Acronis International|access-date=12 July 2016}}</ref>
|-
| 193<br />0xC1 || '''Load Cycle Count''' or  '''Load/Unload Cycle Count''' (Fujitsu) ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Count of load/unload cycles into head landing zone position.<ref name = "Fujitsu MHT20xxAT" /> Some drives use 225 (0xE1) for Load Cycle Count instead.
Western Digital rates their VelociRaptor drives for 600,000 load/unload cycles,<ref>{{Citation | url = http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701282.pdf | title = WD VelociRaptor Spec Sheet | publisher = WD }}</ref> and WD Green drives for 300,000 cycles;<ref>{{Citation | url = http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771438.pdf | title = WD Green Spec Sheet | publisher = WD }}</ref> the latter ones are designed to unload heads often to conserve power. On the other hand, the WD3000GLFS (a desktop drive) is specified for only 50,000 load/unload cycles.<ref>{{cite web |url=http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701260.pdf |title=WD VelociRaptor SATA Hard Drives |year=2008 |access-date=2014-03-31 |publisher=wdc.com }}</ref>

Some laptop drives and "green power" desktop drives are programmed to unload the heads whenever there has not been any activity for a short period, to save power.<ref>{{Citation | url = http://www.thinkwiki.org/wiki/Problem_with_hard_drive_clicking | title = Think | type = wiki | contribution = Problem with hard drive clicking}}</ref><ref>{{cite web
 | url = http://man7.org/linux/man-pages/man8/hdparm.8.html
 | title = hdparm(8) - Linux manual page
 | date = November 2012 | access-date = 2014-03-31
 | publisher = man7.org
 | quote = Get/set the Western Digital (WD) Green Drive's "idle3" timeout value.  This timeout controls how often the drive parks its heads and enters a low power consumption state.  The factory default is eight (8) seconds, which is a very poor choice for use with Linux.  Leaving it at the default will result in hundreds of thousands of head load/unload cycles in a very short period of time.
}}</ref> Operating systems often access the file system a few times a minute in the background,<ref>{{Citation | url = http://bbs.archlinux.org/viewtopic.php?id=66706 | publisher = Arch Linux | title = discussion list | quote = If linux tends to write to /var/log/* every 30s, then the heads can park/unpark every 30s.}}</ref> causing 100 or more load cycles per hour if the heads unload: the load cycle rating may be exceeded in less than a year.<ref>{{Citation | url = http://www.thinkwiki.org/wiki/How_to_reduce_power_consumption#Hard_Drives | type = wiki | publisher = Think | contribution = Hard drives | title = How to Reduce Power Consumption | quote = The files access time update, while mandated by POSIX, is causing lots of disks access; even accessing files on disk cache may wake the ATA or USB bus.}}</ref> There are programs for most operating systems that disable the [[Advanced Power Management]] (APM) and Automatic acoustic management (AAM) features causing frequent load cycles.<ref>{{cite web |url=http://www.kg4cyx.net/mac-os-x-is-beating-your-hard-drives-to-death-heres-the-fix/ |title=Mac OS X is beating your hard drives to death. Here's the fix. |website=Kg4cyx.net |date=11 November 2014|access-date= 3 April 2016}}</ref><ref>{{cite web |url=https://sites.google.com/site/quiethdd/ |title=quietHDD |website=quiethdd|date=13 December 2009 |access-date= 3 April 2016}}</ref>
|-
| 194<br />0xC2 || '''Temperature''' or '''Temperature Celsius''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Indicates the device temperature, if the appropriate sensor is fitted.  Lowest byte of the raw value contains the exact temperature value (Celsius degrees).<ref>{{cite web |url=http://www.z-a-recovery.com/manual/smart.aspx |title=S.M.A.R.T. basics}}</ref>
|-
| 195<br />0xC3 || '''Hardware ECC Recovered''' || {{varies}} 
||| (Vendor-specific raw value.) The raw value has different structure for different vendors and is often not meaningful as a decimal number. For some drives, this number may increase during normal operation without necessarily signifying errors.
|- style="background:#FED;"
| 196<br />0xC4 || '''Reallocation Event Count'''<ref name="Fujitsu MHT20xxAT" /> ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":0" />}}
| Count of remap operations.  The raw value of this attribute shows the total count of attempts to transfer data from reallocated sectors to a spare area. Both successful and unsuccessful attempts are counted.<ref>{{Citation | url = http://kb.acronis.com/content/9132| contribution = S.M.A.R.T.-Attribute: Reallocation Event Count | title = Knowledge Base | publisher = Acronis}}</ref>
|- style="background:#FED;"
| 197<br />0xC5 || '''Current Pending Sector Count'''<ref name="Fujitsu MHT20xxAT" /> ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":0" /><ref name=":2" /><ref name=":4" />}}
|  Count of "unstable" sectors (waiting to be remapped, because of unrecoverable read errors). If an unstable sector is subsequently read successfully, the sector is remapped and this value is decreased. Read errors on a sector will not remap the sector immediately (since the correct value cannot be read and so the value to remap is not known, and also it might become readable later); instead, the drive firmware remembers that the sector needs to be remapped, and will remap it the next time it has been successfully read.<ref>{{Citation |url = http://kb.acronis.com/content/9133|contribution = S.M.A.R.T. Attribute: Current Pending Sector Count|title = Knowledge Base|publisher = Acronis}}</ref> 
However, some drives will not immediately remap such sectors when successfully read; instead the drive will first attempt to write to the problem sector, and if the write operation is successful the sector will then be marked as good (in this case, the "Reallocation Event Count" (0xC4) will not be increased). This is a serious shortcoming, for if such a drive contains marginal sectors that consistently fail only after some time has passed following a successful write operation, then the drive will never remap these problem sectors.
|- style="background:#FED;"
| 198<br />0xC6 || '''(Offline) Uncorrectable Sector Count'''<ref name="Fujitsu MHT20xxAT"/>||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":0" /><ref name=":1" />}}
| The total count of uncorrectable errors when reading/writing a sector. A rise in the value of this attribute indicates defects of the disk surface and/or problems in the mechanical subsystem.<ref name=":0" /><ref name=":4" /><ref name=":2" />
|-
| 199<br />0xC7 || '''UltraDMA CRC Error Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The count of errors in data transfer via the interface cable as determined by ICRC (Interface Cyclic Redundancy Check).
|-
| 200<br />0xC8 || '''Multi-Zone Error Rate''' <ref name="hdat2">{{cite web | first = Lubomir | last = Cabla | date = 2009-08-06 |title=HDAT2 v4.6 User's Manual | edition = 1.1 | url= http://www.hdat2.com/files/hdat2en_v11.pdf}}</ref> ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The count of errors found when writing a sector. The higher the value, the worse the disk's mechanical  condition is.
|-
| 200<br />0xC8 || '''Write Error Rate''' (Fujitsu) ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The total count of errors when writing a sector.<ref name = "smartlinux-attrs">{{cite web | work = SMART Linux project | title = Attributes | publisher = Source forge |url= http://smartlinux.sourceforge.net/smart/attributes.php}}</ref>
|- style="background:#FED;"
| 201<br />0xC9 || '''Soft Read Error Rate''' or<br />'''TA Counter Detected''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
|<br/>[[File:Nuvola apps important.svg|28px|center|link=|alt=Critical]]
{{Center|<ref name=":5">{{Cite web|url=https://kb.acronis.com/content/9137|title=S.M.A.R.T. Attribute: Soft Read Error Rate / Off Track Errors (Maxtor) {{!}} Knowledge Base|website=kb.acronis.com|language=en|access-date=2017-03-19}}</ref>}}
| Count indicates the number of uncorrectable software read errors.<ref name=":5" />
|-
| 202<br />0xCA || '''Data Address Mark errors''' or<br />'''TA Counter Increased''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Count of Data Address Mark errors (or vendor-specific).<ref name=hatfield2005 />
|-
| 203<br />0xCB || '''Run Out Cancel''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The number of errors caused by incorrect checksum during the error correction.
|-
| 204<br />0xCC || '''Soft ECC Correction''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
||| Count of errors corrected by the internal error correction software.<ref name=hatfield2005 />
|-
| 205<br />0xCD || '''Thermal Asperity Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
||| Count of errors due to high temperature.<ref name=hdsentinel>{{Citation | url = http://www.hdsentinel.com/help/en/56_attrib.html | title = S.M.A.R.T. attribute list (ATA)| publisher = HD sentinel}}</ref>
|-
| 206<br />0xCE || '''Flying Height''' ||  
||| Height of heads above the disk surface. If too low, head crash is more likely; if too high, read/write errors are more likely.<ref name=hatfield2005 /><ref>{{cite web|title=9142: S.M.A.R.T. Attribute: Flying Height|url=https://kb.acronis.com/content/9142|website=Acronis Knowledge Base|publisher=Acronis International|access-date=12 July 2016}}</ref>
|-
| 207<br />0xCF || '''Spin High Current''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
||| Amount of surge current used to spin up the drive.<ref name=hdsentinel/>
|-
| 208<br />0xD0 || '''Spin Buzz''' ||  
||| Count of buzz routines needed to spin up the drive due to insufficient power.<ref name=hdsentinel/>
|-
| 209<br />0xD1 || '''Offline Seek Performance''' ||  
||| Drive's seek performance during its internal tests.<ref name =hdsentinel />
|-
| 210<br />0xD2 || '''Vibration During Write''' ||  
||| Found in Maxtor 6B200M0 200GB and Maxtor 2R015H1 15GB disks.
|-
| 211<br />0xD3 || '''Vibration During Write''' ||  
||| A recording of a vibration encountered during write operations.<ref>{{cite web|title=9146: S.M.A.R.T. Attribute: Vibration During Write|url=https://kb.acronis.com/content/9146|website=Acronis Knowledge Base|publisher=Acronis International|access-date=12 July 2016}}</ref>
|-
| 212<br />0xD4 || '''Shock During Write''' ||  
||| A recording of shock encountered during write operations.<ref name=acronis/><ref>{{cite web|title=9147: S.M.A.R.T. Attribute: Shock During Write|url=https://kb.acronis.com/content/9147|website=Acronis Knowledge Base|publisher=Acronis International|access-date=12 July 2016}}</ref>
|-
| 220<br />0xDC || '''Disk Shift''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Distance the disk has shifted relative to the spindle (usually due to shock or temperature). Unit of measure is unknown.<ref name=acronis/>
|-
| 221<br />0xDD || '''G-Sense Error Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The count of errors resulting from externally induced shock and vibration. More typically reported at 0xBF.
|-
| 222<br />0xDE || '''Loaded Hours''' ||  
||| Time spent operating under data load (movement of magnetic head armature).<ref name=acronis/>
|-
| 223<br />0xDF || '''Load/Unload Retry Count''' ||  
||| Count of times head changes position.<ref name=acronis/>
|-
| 224<br />0xE0 || '''Load Friction''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|alt=Lower]]
||| Resistance caused by friction in mechanical parts while operating.<ref name=acronis/>
|-
| 225<br />0xE1 || '''Load/Unload Cycle Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Total count of load cycles<ref name=acronis>{{cite web |url=https://kb.acronis.com/es/taxonomy/term/1644?page=3 |title=S.M.A.R.T. |website=Acronis|date=9 March 2010 |access-date= 1 April 2016}} Samsung, Seagate, IBM (Hitachi), Fujitsu (not all models), Maxtor, Western Digital (not all models)</ref> Some drives use 193 (0xC1) for Load Cycle Count instead. See Description for 193 for significance of this number.
|-
| 226<br />0xE2 || '''Load 'In'-time''' ||  
||| Total time of loading on the magnetic heads actuator (time not spent in parking area).<ref name=acronis/>
|-
| 227<br />0xE3 || '''Torque Amplification Count''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Count of attempts to compensate for platter speed variations.<ref>{{cite web|title=9154: S.M.A.R.T. Attribute: Torque Amplification Count|url=https://kb.acronis.com/content/9154|website=Acronis Knowledge Base|publisher=Acronis International|access-date=12 July 2016}}</ref>
|-
| 228<br />0xE4 || '''Power-Off Retract Cycle''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| The number of power-off cycles which are counted whenever there is a "retract event" and the heads are loaded off of the media such as when the machine is powered down, put to sleep, or is idle.<ref name=hatfield2005 /><ref name="acroniskb"/>
|-
| 230<br />0xE6 || '''GMR Head Amplitude''' (magnetic HDDs), '''Drive Life Protection Status''' (SSDs) ||  
||| Amplitude of "thrashing" (repetitive head moving motions between operations).<ref name=hatfield2005 /><ref>{{cite web|title=9156: S.M.A.R.T. Attribute: GMR Head Amplitude|url=https://kb.acronis.com/content/9156|website=Acronis Knowledge Base|publisher=Acronis International}}</ref>
In solid-state drives, indicates whether usage trajectory is outpacing the expected life curve<ref name="kingston1">{{Citation | title = SMART Attribute Details | url = http://media.kingston.com/support/downloads/MKP_306_SMART_attribute.pdf | type = PDF | publisher = Kingston}}</ref> 
|-
| 231<br />0xE7 || '''Life Left'''  (SSDs) or '''Temperature''' || 
||| Indicates the approximate SSD life left, in terms of program/erase cycles or available reserved blocks.<ref name="kingston1" /> A normalized value of 100 represents a new drive, with a threshold value at 10 indicating a need for replacement. A value of 0 may mean that the drive is operating in read-only mode to allow data recovery.<ref>{{Cite web|url=https://sourceforge.net/p/smartmontools/mailman/message/32246334/|title=S.M.A.R.T. Monitoring Tools / Mailing Lists|website=sourceforge.net|language=en|access-date=2017-03-19}}</ref>

Previously (pre-2010) occasionally used for Drive Temperature (more typically reported at 0xC2). 
|-
| 232<br />0xE8 || '''Endurance Remaining''' or '''Available Reserved Space''' || 
||| Number of physical erase cycles completed on the SSD as a percentage of the maximum physical erase cycles the drive is designed to endure.
Intel SSDs report the available reserved space as a percentage of the initial reserved space.
|-
| 233<br />0xE9 || '''Media Wearout Indicator''' (SSDs) or '''Power-On Hours''' || 
||| Intel SSDs report a normalized value from 100, a new drive, to a minimum of 1. It decreases while the NAND erase cycles increase from 0 to the maximum-rated cycles.

Previously (pre-2010) occasionally used for Power-On Hours (more typically reported in 0x09).
|-
| 234<br />0xEA || '''Average erase count AND  Maximum Erase Count''' || 
||| Decoded as: byte 0-1-2 = average erase count (big endian) and byte 3-4-5 = max erase count (big endian).<ref>{{cite web | type = log | publisher = Source forge | url=https://www.smartmontools.org/ticket/171|work= Smartmontools | title = Ticket 171}}</ref>

|-
| 235<br />0xEB || '''Good Block Count AND System(Free) Block Count''' || 
||| Decoded as: byte 0-1-2 = good block count (big endian) and byte 3-4 = system (free) block count.

|-
| 240<br />0xF0 || '''Head Flying Hours''' or ''''''Transfer Error Rate'''''' (Fujitsu) ||  
||| Time spent during the positioning of the drive heads.<ref name=hatfield2005 /><ref>{{cite web|title=9157: S.M.A.R.T. Attribute: Head Flying Hours / Transfer Error Rate (Fujitsu)|url=https://kb.acronis.com/content/9157|website=Acronis Knowledge Base|publisher=Acronis International}}</ref> Some Fujitsu drives report the count of link resets during a data transfer.<ref>{{cite web|url=http://pdfstream.manualsonline.com/2/20e501aa-595c-46fe-bbac-2088887ceffe.pdf|title=MHY2250BH, MHY2200BH, MHY2160BH, MHY2120BH, MHY2100BH, MHY2080BH, MHY2060BH, MHY2040BH Disk Drives, Product/Maintenance Manual|publisher=Fujitsu Limited|id=C141-E262-01EN}}</ref>
|-
| 241<br />0xF1 || '''Total LBAs Written''' ||  
||| Total count of LBAs written.
|-
| 242<br />0xF2 || '''Total LBAs Read''' ||  
||| Total count of LBAs read.<br />Some S.M.A.R.T. utilities will report a negative number for the raw value since in reality it has 48 bits rather than 32.
|-
| 243<br />0xF3 || '''Total LBAs Written Expanded''' ||  
||| The upper 5 bytes of the 12-byte total number of LBAs written to the device. The lower 7 byte value is located at attribute 0xF1.<ref>{{Citation | publisher = Delkin Devices | date = 2013| title = SlimSATA SSD Mini-SATA Embedded Flash Module  | type = Engineering Specification | number = L500109 | url = http://delkinoem.com/oem-engineering-specs-product-docs/Industrial-SlimSATA-solid-state-drive-specification.pdf }}</ref>
|-
| 244<br />0xF4 || '''Total LBAs Read Expanded''' ||  
||| The upper 5 bytes of the 12-byte total number of LBAs read from the device. The lower 7 byte value is located at attribute 0xF2.<ref>{{Citation | publisher = Delkin Devices | date = 2013| title = SlimSATA SSD Mini-SATA Embedded Flash Module  | type = Engineering Specification | number = L500109 | url = http://delkinoem.com/oem-engineering-specs-product-docs/Industrial-SlimSATA-solid-state-drive-specification.pdf }}</ref>
|-
| 249<br />0xF9 || '''NAND Writes (1GiB)''' ||  
||| Total NAND Writes.  Raw value reports the number of writes to NAND in 1&nbsp;GB increments.<ref>{{Citation | publisher = Intel | date = February 2012| title = Intel Solid-state Drive 520 Series Product Specification | type = product manual | number = 325968–001US | url = http://download.intel.com/newsroom/kits/ssd/pdfs/intel_ssd_520_product_spec_325968.pdf }}</ref>
|-
| 250<br />0xFA || '''Read Error Retry Rate''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Count of errors while reading from a disk.<ref name=acronis/>
|-
| 251<br />0xFB || '''Minimum Spares Remaining''' ||  
||| The Minimum Spares Remaining attribute indicates the number of remaining spare blocks as a percentage of the total number of spare blocks available.<ref name="google_code_hdd_guardian">{{cite web|url=https://code.google.com/p/hddguardian/wiki/Smart_Modular_SMART_attributes|title=SMART Modular Technologies S.M.A.R.T. attributes - A new Windows interface for smartctl|work=google.com}}</ref>
|-
| 252<br />0xFC || '''Newly Added Bad Flash Block''' ||  
||| The Newly Added Bad Flash Block attribute indicates the total number of bad flash blocks the drive detected since it was first initialized in manufacturing.<ref name="google_code_hdd_guardian" />
|-
| 254<br />0xFE || '''Free Fall Protection''' ||{{Center|Low}}[[Image:Dark Green Arrow Down.svg|18px|center|link=|alt=Lower]]
||| Count of "Free Fall Events" detected.<ref>{{Citation | publisher = Seagate | date= September 2007 | title = Momentus 7200.2 SATA | type = product manual | number = 100451238 | edition = D | id= Hitachi Document Part Number S13K-1055-20 | url= http://www.seagate.com/staticfiles/support/disc/manuals/notebook/momentus/7200.2/100451238d.pdf}}</ref>
|}

=== {{Anchor|TEC}}Threshold Exceeds Condition ===
Threshold Exceeds Condition (TEC) is an estimated date when a critical drive statistic attribute will reach its threshold value. When Drive Health software reports a "Nearest T.E.C.", it should be regarded as a "Failure date". Sometimes, no date is given and the drive can be expected to work without errors.<ref name = "Drivehealth's FAQ">{{Citation | url = http://www.drivehealth.com/faq.html | title = Drive health | contribution = FAQ | access-date = October 4, 2011}}</ref>

To predict the date, the drive tracks the rate at which the attribute changes.  Note that TEC dates are only estimates; hard drives can and do fail much sooner or much later than the TEC date.<ref name="Altrixsoft FAQ">{{Citation | url = http://www.altrixsoft.com/en/support/help/hddinsp/tec%20and%20smart.php | title = The interpretation of the TEC and the SMART | publisher = Altrix soft | access-date = October 4, 2011}}</ref>

== Self-tests ==
S.M.A.R.T. drives may offer a number of self-tests:<ref>{{Citation | chapter-url = http://smartmontools.sourceforge.net/man/smartctl.8.html | chapter-format = manpage | title = SMARTCTL | chapter = self-tests: "SMART RUN/ABORT OFFLINE TEST AND SELF-TEST OPTIONS: -t TEST, --test=TEST" | url-status = dead | archive-url = https://web.archive.org/web/20090715005747/http://smartmontools.sourceforge.net/man/smartctl.8.html | archive-date = 2009-07-15 }}</ref><ref>{{Citation | url = http://hddscan.com/ | title = HDDScan}} – free HDD test utility with USB flash and RAID support.</ref><ref>{{Citation | publisher = T10 | url = http://www.t10.org/ftp/t10/document.99/99-179r0.pdf | title = Hard Drive Self-tests | first = Mark | last = Evans | place = Milpitas, CA US | date = 26 April 1999}}</ref>

'''Short'''
: Checks the electrical and mechanical performance as well as the read performance of the disk.  Electrical tests might include a test of buffer RAM, a read/write circuitry test, or a test of the read/write head elements.   Mechanical test includes seeking and servo on data tracks.  Scans small parts of the drive's surface (area is vendor-specific and there is a time limit on the test).  Checks the list of pending sectors that may have read errors, and it usually takes under two minutes.

'''Long/extended'''
: A longer and more thorough version of the short self-test, scanning the entire disk surface with no time limit. This test usually takes several hours, depending on the read/write speed of the drive and its size.

'''Conveyance'''
: Intended as a quick test to identify damage incurred during transporting of the device from the drive manufacturer to the computer manufacturer.<ref>{{Citation | publisher = T10 | url = http://www.t10.org/t13/technical/e01137r0.pdf | title = Proposal for Extensions To Drive Self Test | first = Darrin | last = Bulik | place = Lake Forest, {{wipe|California}} | date = Sep 24, 2001 | url-status = dead | archive-url = https://web.archive.org/web/20110928091120/http://www.t10.org/t13/technical/e01137r0.pdf | archive-date = 2011-09-28 }}</ref> Only available on ATA drives, and it usually takes several minutes.

'''Selective'''
: Some drives allow selective self-tests of just a part of the surface.<ref>{{Citation | publisher = T10 | url = http://www.t10.org/t13/technical/e01139r0.pdf | title = Proposal for a Selective Self-test | first = Pete | last = McLean | place = Longmont, CO | date = 23 October 2001 | url-status = dead | archive-url = https://web.archive.org/web/20110928091148/http://www.t10.org/t13/technical/e01139r0.pdf | archive-date = 28 September 2011 }}</ref>

The self-test logs for SCSI and ATA drives are slightly different.  It is possible for the long test to pass even if the short test fails.<ref>{{cite web| url = http://www.hardwarecanucks.com/forum/storage/23040-hdd-fails-s-m-r-t-short-test-but-passes-long-test.html | title = HDD fails S.M.A.R.T. short test, but passes long test? | publisher =Hardware Canucks | access-date= 2013-01-15}}</ref>

The drive's self-test log can contain up to 21 read-only entries. When the log is filled, old entries are removed.<ref>[https://sourceforge.net/p/smartmontools/mailman/message/10781945/], Smartmontools mailing lists</ref>

== See also ==

* [[Engineering:Comparison of S.M.A.R.T. tools|Comparison of S.M.A.R.T. tools]]
* [[Data scrubbing]]
* [[Software:Disk utility|Disk utility]]
* [[Software:List of disk partitioning software|List of disk partitioning software]]
* Predictive failure analysis
* [[System monitor]]
* {{section link|Optical_disc#Surface_error_scanning}}

== References ==
{{Reflist|30em}}

== Further reading ==
* {{Citation | editor-last = Stephens | editor-first = Curtis E | work = ATA Command Set 2 | title = ATA/ATAPI Command Set - 2 (ACS-2) | type = working draft | edition = 7 | publisher = ANSI INCITS | date = June 22, 2011 | url = http://www.t13.org/documents/UploadedDocuments/docs2011/d2015r7-ATAATAPI_Command_Set_-_2_ACS-2.pdf | page = 73 }}.
* {{cite web | url = http://www.siguardian.com/products/siguardian/on_line_help/s_m_a_r_t_attribute_meaning.html | archive-url = https://web.archive.org/web/20110226194620/http://www.siguardian.com/products/siguardian/on_line_help/s_m_a_r_t_attribute_meaning.html | title = S.M.A.R.T. attribute meaning | website = siguardian.com | access-date = February 3, 2006 | archive-date = February 26, 2011}}
* {{cite web | first = Zbigniew | last = Chlondowski | url = http://smartlinux.sourceforge.net/smart/attributes.php | title = S.M.A.R.T. Site: attributes reference table | publisher = S.M.A.R.T. Linux | access-date = January 17, 2007}}
* {{cite web | publisher = Ariolic | year = 2007 | url = http://www.ariolic.com/activesmart/smart-attributes/ | title = S.M.A.R.T. attributes meaning | access-date = October 26, 2007}}
* {{cite web | work = H.D.S. Hungary | year = 2007 | url = http://www.hdsentinel.com/smart | title = Can we believe SMART? | access-date = June 4, 2008}}
* {{cite magazine | first = Bruce | last = Allen | year = 2004 | url = http://www.linuxjournal.com/article/6983 | title = Monitoring Hard Disks with SMART | magazine = Linux Journal| access-date = August 8, 2010}}

== External links ==

* {{Citation | url = http://www1.ucsc.edu/news_events/press_releases/archive/99-00/09-99/smart_software.htm | title = UC Santa Cruz and Quantum release S.M.A.R.T. software for Linux | publisher = Michael Cornwell}}.
* {{Citation | url = https://sourceforge.net/projects/smartsuite/ | title = UCSC SMART suite | publisher = [[Software:SourceForge|SourceForge]]}} by: [http://sourceforge.net/users/cornwell cornwell].
* {{Citation | url = https://sourceforge.net/p/smartmontools/mailman/message/7330862/ | title = How does smartmontools differ from smartsuite? | publisher = [[Software:SourceForge|SourceForge]]}}.
* {{Citation | url = https://sourceforge.net/projects/smartmontools/ | title =  S.M.A.R.T. Monitoring Tools | publisher = [[Software:SourceForge|SourceForge]]}} by: ballen4705.
* {{Citation | url = https://www.smartmontools.org/wiki | title = smartmontools & smartsuite | publisher = smartmontools.org}}.
*GSmartControl is a [[Graphical user interface|GUI]] for smartctl (part of smartmontools) by Alexander Shaduri
* {{Citation | url = http://www.pc-king.co.uk/tips3.htm | title = How S.M.A.R.T. is your hard drive? | publisher = pc-king.co.uk | place = {{wipe|United Kingdom}}}}.
* {{Citation | url = http://karuppuswamy.com/wordpress/2010/05/19/how-to-predict-hard-disk-failure-in-ubuntu-with-3-clicks/ | title = How to predict hard disk failure (SMART Report) | date = 2010-05-19}} with [[Software:GNOME Disks|Palimpsest]] (originally by Red Hat)
* {{Citation | url = http://wdc.custhelp.com/app/answers/detail/a_id/251/ | publisher = Western Digital | title = KB251: Understanding S.M.A.R.T. and S.M.A.R.T. failure and errors}}.
* {{Citation | url = http://www.hdsentinel.com/smart/index.php | title = How does S.M.A.R.T. function of hard disks Work?}}.
* [https://www.backblaze.com/blog/hard-drive-smart-stats/ Hard Drive SMART Stats], a large-scale field report
* [http://t1.daumcdn.net/brunch/service/user/axm/file/zRYOdwPu3OMoKYmBOby1fEEQEbU.pdf Seagate SMART Attribute Specification]
* [http://t1.daumcdn.net/brunch/service/user/axm/file/Vw3RJSZllYbDc86ssL6bofiL4r0.pdf Normal SATA SMART Attribute Behavior (Seagate)]
* [https://github.com/linuxhw/SMART Large collection of S.M.A.R.T. reports]

[[Category:Computer storage technologies]]
[[Category:SCSI]]

{{Sourceattribution|S.M.A.R.T.|1}}