What is S.M.A.R.T? |

S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is an interface between the BIOS and a computers hard disk. It is a feature of the Enhanced Integrated Drive Electronics (EIDE) technology that controls access to the hard drive. If S.M.A.R.T is enabled when a computer is set up, the BIOS can receive analytical information from the hard drive and determine whether to send the user a warning message about possible future failure of the hard drive.

S.M.A.R.T monitors a set of drive attributes, such as temperature, throughput performance and the number of hours the drive has been powered on. It compares these attributes to a corresponding set of thresholds. If an attribute drops below its threshold, the drive is no longer considered fit for use and should be replaced immediately. Not all attributes are available on all drives, however - it is the responsibility of the drive manufacturer to include S.M.A.R.T support.

The S.M.A.R.T attributes are listed here.

ID | Name | Raw value is better when* | Description**
1 | Raw Read Error Rate | Lower | Represents the rate of uncorrected read errors
2 | Throughput Performance | Higher | Represents the throughput performance of the drive. I.e. The speed at which the drive is reading and writing data.
3 | Spin Up Time | Lower | Represents the average amount of time required to spin up the drive spindle to operational speed from a stopped state.
4 | Start/Stop Count | Lower | Represents the number of start/stop cycles for the drive. The raw value indicates the count of start/stop cycles for the drive. The drive being powered on/off or suspended/woken up are considered as start/stop cycles.
5 | Reallocated Sector Count | Lower | Represents the amount of spare sector pool available. Spare sectors are used to replace sectors that became bad for some reason (for instance, if a read error occurs). Therefore the more sectors reallocated, the worse the condition of the drive.
7 | Seek Error Rate | Lower | Represents the number of seek errors. Each time the drive attempts a seek operation, but fails to position its head correctly, the seek error rate increases.
8 | Seek Time Performance | Higher | Represents how efficiently the drive is performing seek operations. A low value indicates problems with the drive subsystem, for instance the servo responsible for positioning the head.
9 | Power On Hours Count | Higher | This is an informative attribute, the raw value of which displays the number of hours the drive has been powered on for.
A | Spin Retry Count | Lower | Represents the number of times a drive fails to spin its spindle up to operation speed on the first attempt.
B | Calibration Retry Count | Higher | Calibration is the act of repositioning the drive read/write head to cylinder 0. This value represents the number of times a calibration has failed on the first attempt.
C | Power Cycle Count | Lower | Informative attribute, the raw value of which represents the number of drive power on/drive power off cycles for the disk.
D | Soft Read Error Rate | Lower | Uncorrected read errors reported to the operating system.
BE | Temperature related | Unknown | To the best of our knowledge, there are 2 definitions, both related to temperature: "Airflow Temperature" and "Temperature difference from 100". The definition depends on the vendor, and in some cases the drive model. In any case, if the threshold is exceeded, it is temperature related.
BF | G-Sense Error Rate | Lower | Frequency of mistakes as a result of impact loads
C0 | Power-off Retract Count | Lower | Number of times the heads are loaded off the media. Heads can be unloaded without actually powering off.
C1 | Load/Unload Cycle | Lower | Count of load/unload cycles into head landing zone position.
C2 | Temperature | Lower | Informative attribute, the raw value of which represents the current temperature in Celsius of the drive.
C3 | Hardware ECC Recovered | Higher | Time between ECC-corrected errors.
C4 | Reallocation Event Count | Lower | Represents the number of reallocation events, which have taken place. Sometimes multiple sectors are reallocated together – this corresponds to one reallocation event. (See also: Reallocated Sector Count and Current Pending Sector Count).
C5 | Current Pending Sector Count | Lower | Represents the number of sectors currently pending reallocation.
C6 | Uncorrectable Sector Count | Lower | The total number of uncorrectable errors when reading/writing a sector.
C7 | UltraDMA CRC Error Count | Lower | Represents the number of CRC error found in the Ultra DMA high-speed transfer mode. (CRC stands for Cyclic Redundancy Check and is data verification algorithm which uses polynomial checksums).
C8 | Write Error Count | Lower | Represents the rate of uncorrected write errors. Lower raw values indicate that there is a problem with either disk surface or read/write heads.
C9 | Soft Read Error Rate | Lower | Number of off-track errors.
CA | Data Address Mark errors | Lower | Number of Data Address Mark errors
CB | Run Out Cancel | Lower | Number of ECC errors
CC | Soft ECC Correction | Lower | Number of errors corrected by software ECC.
CD | Thermal asperity rate(TAR) | Lower | Number of thermal asperity errors.
CE | Flying Height | Unknown | Height of heads above the disk surface.
CF | Spin High Current | Unknown | Amount of high current used to spin up the drive.
D0 | Spin Buzz | Unknown | Number of buzz routines to spin up the drive
D1 | Offline Seek Performance | Unknown | Drive’s seek performance during offline operations
DC | Disk Shift | Lower | Distance the disk has shifted relative to the spindle (usually due to shock).
DD | G-Sense Error Rate | Lower | The number of errors resulting from externally-induced shock & vibration.
DE | Loaded Hours | Lower | Time spent operating under data load (movement of magnetic head armature)
DF | Load/Unload Retry Count | Unknown | Number of times head changes position.
E0 | Load Friction | Lower | Resistance caused by friction in mechanical parts while operating.
E1 | Load/Unload Cycle Count | Lower | Total number of load cycles
E2 | Load 'In'-time | Unknown | Total time of loading on the magnetic heads actuator (time not spent in parking area).
E3 | Torque Amplification Count | Unknown | Number of attempts to compensate for platter speed variations
E4 | Power-off Retract Count | Lower | The number of times the magnetic armature was retracted automatically as a result of cutting power.
E6 | GMR Head Amplitude | Unknown | Amplitude of "thrashing" (distance of repetitive forward/reverse head motion)
E7 | Temperature | Unknown | Drive Temperature, unknown units.
F0 | Head Flying Hours | Unknown | Time while head is positioning
FA | Read Error Retry Rate | Lower | Number of errors while reading from a disk

*Raw values are an absolute reading of an attribute as reported by the hard disk; what constitutes a high or a low value will differ between attributes and hard disk models. If you are unsure of how to interpret these values it is better to observe the normalized value.

**Descriptions for several of the attributes are taken from various sources on the web including wikipedia.org.