Self-Monitoring, Analysis and Reporting Technology

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Another example of another software showing the hard drive's health condition and the SMART values

Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T., often written as SMART) is a monitoring system included in computer hard disk drives (HDDs) and solid-state drives (SSDs).[1] 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 action can be taken to prevent data loss, and the failing drive can be replaced and data integrity maintained.


Hard disk and other storage drives are subject to failures (see hard disk drive failure) which can be classified into 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.[2] 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:[3]

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.


A field study at Google[4] 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.[5]

History and predecessors[edit]

An early hard disk monitoring technology was introduced by IBM in 1992 in its IBM 9337 Disk Arrays for AS/400 servers using IBM 0662 SCSI-2 disk drives.[6] 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 Compaq and disk drive manufacturers Seagate, Quantum, and Conner.[7] 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.[8] It was supported by IBM, by Compaq's development partners Seagate, Quantum, and Conner, and by 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.[9] 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[edit]

A 3.5-inch Serial ATA hard disk drive
A 2.5-inch Serial ATA solid-state drive

The technical documentation for S.M.A.R.T. is in the AT Attachment (ATA) standard. First introduced in 1994,[10] the ATA standard has gone through multiple revisions. Some parts of the original S.M.A.R.T. specification by the Small Form Factor (SFF) Committee were added to ATA-3,[11] 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.[11] Albeit, manufacturers have kept the capability to retrieve the attributes' value. The most recent ATA standard, ATA-8, was published in 2004.[12] It has undergone regular revisions,[13] the latest being in 2011.[14] 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.[15]

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.[16]

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.[17]

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 232 ms = 49.71 days[18])

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[edit]

Lack of common interpretation[edit]

Many motherboards display a warning message when a disk drive is approaching failure. Although an industry standard exists among most major hard drive manufacturers,[3] issues remain due to attributes intentionally left undocumented to the public in order to differentiate models between manufacturers.[19][17] 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."[17]

Visibility to host systems[edit]

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 (SCSI, Fibre Channel, ATA, SATA, SAS, SSA, 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 Windows platform, many programs designed to monitor and report S.M.A.R.T. information will function only under an administrator account.

BIOS and Windows (Windows Vista and later) may detect S.M.A.R.T. status of hard disk drives and solid state drives, and give a prompt if the S.M.A.R.T. status is bad.[20]

In ATA[edit]

ATA S.M.A.R.T. attributes[edit]

Each drive manufacturer defines a set of attributes,[21][22] and sets threshold values beyond which attributes should not pass under normal operation.[17] Each attribute has:[23]

  • 1 byte for the ID (1 through 254)
  • 2 bytes for status flags
  • 1 byte of normalized value, which ranges from 1 to 253 (higher is usually better, but vendors are allowed to vary; the threshold entry stored elsewhere describes which direction is better). The initial normalized value of attributes is 100 but can vary between manufacturer.
  • 8 bytes "vendor-specific".

In practice, however, the full "vendor-specific" field is not used as-is. Instead, one of the following occurs:[24]

  • In the 7-byte setup, the first byte of "vendor-specific" is used to store a "worst" normalized value, leaving 7 bytes for vendor data.
  • In the 6-byte setup, the first byte of "vendor-specific" is used to store a "worst" normalized value and the last byte "reserved", leaving 6 bytes.
  • In the 8-byte setup, the normalized byte is added to the field while the last byte is reserved.

In any case, the vendor field, also commonly called a "raw value", may be displayed as a decimal or hexadecimal number; its meaning is entirely up to the drive manufacturer (but often corresponds to counts or a physical unit, such as degrees Celsius or seconds).[25]

If one or more "current value" is smaller than "threshold value" (except the "threshold value" is 0), that will reported as "drive failure".

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

Known ATA S.M.A.R.T. attributes[edit]

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[26]), 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.

ID 193
Attribute code in decimal and
hexadecimal notations
Higher raw value is better
Lower raw value is better
Denotes a Critical attribute.
Specific values may predict drive failure
ID Attribute name Ideal ! Description
Read Error Rate


(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.[27]
Throughput Performance
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.
Spin-Up Time
Average time of spindle spin up (from zero RPM to fully operational [milliseconds]).
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.[28]
Reallocated Sectors Count

Count of reallocated sectors. The raw value represents a count of the bad sectors that have been found and remapped.[32] 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.[29][33] If Raw value of 0x05 attribute is higher than its Threshold value, that will reported as "drive warning".[34]
Read Channel Margin Margin of a channel while reading data. The function of this attribute is not specified.
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.[27]
Seek Time Performance
Average performance of seek operations of the magnetic heads. If this attribute is decreasing, it is a sign of problems in the mechanical subsystem.
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.[35]

"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."[36]

On some pre-2005 drives, this raw value may advance erratically and/or "wrap around" (reset to zero periodically).[37]

Spin Retry Count

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.
Recalibration Retries or Calibration Retry Count
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.
Power Cycle Count This attribute indicates the count of full hard disk power on/off cycles.
Soft Read Error Rate
Uncorrected read errors reported to the operating system.
Current Helium Level
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.[39]
Helium Condition Lower Specific to MG07+ drives from Toshiba. These values measures 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.[40]
Helium Condition Upper
Available Reserved Space See attribute E8.[41]
SSD Program Fail Count (Kingston) The total number of flash program operation failures since the drive was deployed.[42] Identical to attribute 181.
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.
SSD Wear Leveling Count Counts the maximum worst erase count on any block.
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.[43]
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.[43]

Erase Fail Count S.M.A.R.T. parameter indicates a number of flash erase command failures.[44]
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.
Used Reserved Block Count "Pre-Fail" attribute used at least in Samsung devices.
Used Reserved Block Count Total "Pre-Fail" attribute used at least in Samsung devices.[45]
Unused Reserved Block Count Total "Pre-Fail" attribute used at least in HP devices.
Program Fail Count Total or Non-4K Aligned Access Count
(Flash Memory) Total number of Flash program operation failures since the drive was deployed (indicating old age).[46]

(HDD, Advanced Format) 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 (indicating bad software configuration).[47]

Erase Fail Count "Pre-Fail" Attribute used at least in Samsung devices.
SATA Downshift Error Count or Runtime Bad Block
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.[48] 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.[49]
End-to-End error / IOEDC

This attribute is a part of 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.[51]
Head Stability Western Digital attribute.
Induced Op-Vibration Detection Western Digital attribute.
Reported Uncorrectable Errors

The count of errors that could not be recovered using hardware ECC (see attribute 195).[52]
Command Timeout

The count of aborted operations due to HDD timeout. Normally this attribute value should be equal to zero.[53]
High Fly Writes
HDD manufacturers implement a 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[2] 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.[54]

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.
G-sense Error Rate
The count of errors resulting from externally induced shock and vibration.
Power-off Retract Count, Emergency Retract Cycle Count (Fujitsu),[55] or Unsafe Shutdown Count
Number of power-off or emergency retract cycles.[17][56]
Load Cycle Count or Load/Unload Cycle Count (Fujitsu)
Count of load/unload cycles into head landing zone position.[55] Some drives use 225 (0xE1) for Load Cycle Count instead.

Western Digital rates their VelociRaptor drives for 600,000 load/unload cycles,[57] and WD Green drives for 300,000 cycles;[58] 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.[59]

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.[60][61] Operating systems often access the file system a few times a minute in the background,[62] causing 100 or more load cycles per hour if the heads unload: the load cycle rating may be exceeded in less than a year.[63] There are programs for most operating systems that disable the Advanced Power Management (APM) and Automatic acoustic management (AAM) features causing frequent load cycles.[64][65]

Temperature or Temperature Celsius
Indicates the device temperature, if the appropriate sensor is fitted. Lowest byte of the raw value contains the exact temperature value (Celsius degrees).[66]
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.[27]
Reallocation Event Count[55]

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.[67]
Current Pending Sector Count[55]

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.[68]

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. If Raw value of 0xC5 attribute is higher than its Threshold value, that will reported as "drive warning".[69][70]

(Offline) Uncorrectable Sector Count[55]

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.[4][53][50]
UltraDMA CRC Error Count
The count of errors in data transfer via the interface cable as determined by ICRC (Interface Cyclic Redundancy Check).
Multi-Zone Error Rate [71]
The count of errors found when writing a sector. The higher the value, the worse the disk's mechanical condition is.
Write Error Rate (Fujitsu)
The total count of errors when writing a sector.[72]
Soft Read Error Rate or
TA Counter Detected

Count indicates the number of uncorrectable software read errors.[73]
Data Address Mark errors or
TA Counter Increased
Count of Data Address Mark errors (or vendor-specific).[17]
Run Out Cancel
The number of errors caused by incorrect checksum during the error correction.
Soft ECC Correction
Count of errors corrected by the internal error correction software.[17]
Thermal Asperity Rate
Count of errors due to high temperature.[74]
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.[17][75]
Spin High Current
Amount of surge current used to spin up the drive.[74]
Spin Buzz Count of buzz routines needed to spin up the drive due to insufficient power.[74]
Offline Seek Performance Drive's seek performance during its internal tests.[74]
Vibration During Write Found in Maxtor 6B200M0 200GB and Maxtor 2R015H1 15GB disks.
Vibration During Write A recording of a vibration encountered during write operations.[76]
Shock During Write A recording of shock encountered during write operations.[42][77]
Disk Shift
Distance the disk has shifted relative to the spindle (usually due to shock or temperature). Unit of measure is unknown.[42]
G-Sense Error Rate
The count of errors resulting from externally induced shock and vibration. More typically reported at 0xBF.
Loaded Hours Time spent operating under data load (movement of magnetic head armature).[42]
Load/Unload Retry Count Count of times head changes position.[42]
Load Friction
Resistance caused by friction in mechanical parts while operating.[42]
Load/Unload Cycle Count
Total count of load cycles[42] Some drives use 193 (0xC1) for Load Cycle Count instead. See Description for 193 for significance of this number.
Load 'In'-time Total time of loading on the magnetic heads actuator (time not spent in parking area).[42]
Torque Amplification Count
Count of attempts to compensate for platter speed variations.[78]
Power-Off Retract Cycle
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.[17][56]
GMR Head Amplitude (magnetic HDDs), Drive Life Protection Status (SSDs) Amplitude of "thrashing" (repetitive head moving motions between operations).[17][79]

In solid-state drives, indicates whether usage trajectory is outpacing the expected life curve[80]

Life Left (SSDs) or Temperature Indicates the approximate SSD life left, in terms of program/erase cycles or available reserved blocks.[80] 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.[81]

Previously (pre-2010) occasionally used for Drive Temperature (more typically reported at 0xC2).

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.

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).

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).[82]
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.
Head Flying Hours or 'Transfer Error Rate' (Fujitsu) Time spent during the positioning of the drive heads.[17][83] Some Fujitsu drives report the count of link resets during a data transfer.[84]
Total LBAs Written or Total Host Writes Total count of LBAs written. Some SSD (for example, manufacture by Western Digital and Seagate) use 1GiB as unit of this attribute.
Total LBAs Read or Total Host Reads Total count of LBAs read.
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. Some SSD (for example, manufacture by Western Digital and Seagate) use 1GiB as unit of this attribute.
Total LBAs Written Expanded or Total Host Writes 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.[85]
Total LBAs Read Expanded or Total Host Reads 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.[86]


Remaining Rated Write Endurance
Certified Dell SSDs use this for write endurance.
Cumulative host sectors written (Micron) LBA written due to computer request.[87]
Host program page count (Micron) NAND pages written due to computer request.[88]
Background program page count (Micron) NAND pages written due to background operations (e.g. garbage collection).[88]
NAND Writes (1GiB) Total NAND Writes. Raw value reports the number of writes to NAND in 1 GB increments.[89]
Read Error Retry Rate
Count of errors while reading from a disk.[42]
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.[90]
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.[90]
Free Fall Protection
Count of "Free Fall Events" detected.[91]


GP Log 0x04: Device Statistics
Page Offset Description
0x01 0x08 Lifetime Power-On Resets
0x01 0x10 Power-on Hours
0x01 0x18 Logical Sectors Written
0x01 0x28 Logical Sectors Read
0x05 0x08 Current Temperature
0x05 0x20 Highest Temperature
0x05 0x28 Lowest Temperature
0x05 0x58 Specified Maximum Operating Temperature
0x05 0x68 Specified Minimum Operating Temperature
0x07 0x08 Percentage Used Endurance Indicator

SMART Command Transport[edit]

Threshold Exceeds Condition[edit]

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.[92]

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.[93]

In NVMe[edit]

NVMe specification has defined unified S.M.A.R.T. attributes for different drive manufacturers. The data is present in a log page of 512 bytes long.[94]

Known NVMe S.M.A.R.T. attributes[edit]

Offset Length Attribute name Description
1 Critical Warning Critical warnings for the state of the controller.

Bit definition:
Bit 00, value 1: Available spare is below threshold.
Bit 01, value 1: Temperature is over threshold.
Bit 02, value 1: Drive reliability is degraded.
Bit 03, value 1: Drive is in read only mode.
2 Composite Temperature Temperature in kelvins representing the current composite temperature of the controller and its namespace(s).
1 Available Spare Percentage of available spare.
1 Available Spare Threshold Percentage of available spare threshold.
1 Percentage Used Percentage of drive life used.
25 Reserved
16 Data Units Read Number of 512-byte data units the host has read from the controller. This value does not include metadata. This value is reported in thousands (i.e., a value of 1 corresponds to 1000 units of 512 bytes written) and is rounded up.
16 Data Units Written Number of 512-byte data units the host has written to the controller. This value does not include metadata. This value is reported in thousands (i.e., a value of 1 corresponds to 1000 units of 512 bytes written) and is rounded up.
16 Host Read Commands Number of read commands completed by the controller.
16 Host Write Commands Number of write commands completed by the controller.
16 Controller Busy Time Amount of time the controller is busy with I/O commands.
16 Power Cycles Number of power cycles.
16 Power On Hours Number of power-on hours, excluding time powered on in non-operational power state.
16 Unsafe Shutdowns Number of unsafe shutdowns. Incremented when a Shutdown Notification is not received prior to loss of power.
16 Media Errors Number of occurrences where the controller detected an unrecovered data integrity error, including uncorrectable ECC, CRC checksum failure, or LBA tag mismatch.
16 Number of Error Information Log Entries Number of Error Information log entries over the life of the controller.
4 Warning Composite Temperature Time
4 Critical Composite Temperature Time
2×8 Temperature Sensor 1–8
4×2 Thermal Management Temperature 1/2 Transition Count
4×2 Total Time For Thermal Management Temperature 1/2
280 Reserved

In SCSI[edit]

The SCSI standard does not mention the term "S.M.A.R.T." except in one place, but the equivalent logging/failure-prediction functionality is available in standard log pages prescribed by SPC-4.[15] There is also space for vendor-specific log pages. Log pages are variable-length.[95]

List of SCSI log pages[95]
Code Name Description
00h Supported log pages
01h Buffer Over-Run/Under-Run
02h Write Error Counter
03h Read Error Counter
04h Read Reverse Error Counter
05h Verify Error Counter
06h Non-Medium Error
07h Last n Error Events
0Bh Last n Deferred Errors or Asynchronous Event
0Dh Temperature
0Eh Start-Stop Cycle Counter
0Fh Application Client
10h Self-Test Results
15h Background Scan Results
18h Protocol Specific Port
2Fh Informational Exceptions Provides two kinds of warnings: impending failure warning based on a vendor-defined threshold (similar to ATA SMART normalized values) and temperature warnings.

SCSI has a specialized set of S.M.A.R.T. features for tape drives known as TapeAlert defined in SMC-2.[15] SCSI offers self-testing, similar to ATA.[15]

Information related to the reallocation of bad sectors is provided not via a log page, but via the READ DEFECT DATA command. In addition to a grand total, this command provides information about which specific sectors were allocated and why.[95]


S.M.A.R.T. drives may offer a number of self-tests:[96][97][98]

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.
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. It is possible for the long test to pass even if the short test fails.[99]
Intended as a quick test to identify damage incurred during transporting of the device from the drive manufacturer to the computer manufacturer.[100] Only available on ATA drives, and it usually takes several minutes.
Some ATA drives allow selective self-tests of just a part of the surface.[101] There is a dedicated log for selective test results, separate from the main self-test log.
Background scan
SCSI drives have the ability to schedule periodic full-surface self-tests known as a background media scan (BMS). The sdparm program may be used to adjust whether to run the scans (EN_BMS) and various parameters for the scan (e.g. period, idle time before run). The drive remains operable during the test.[102] There is a dedicated log for background scan results, separate from the self-test log.
Offline data collection
ATA drives may support a periodic short operation called "offline data collection". Although this feature is marked "obsolete", many modern hard drives retain this feature. The drive remains operable during collection and any result is reflected only in SMART attributes (some attributes only update when "offline").[103]

Drives remain operable during self-test, unless a "captive" option (ATA only) is requested.[96]

The self-test logs for SCSI and ATA drives are slightly different.

The ATA drive's self-test log can contain up to 21 read-only entries. When the log is filled, old entries are removed.[104]

See also[edit]


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Further reading[edit]

External links[edit]