Self-Monitoring, Analysis and Reporting Technology

Self-Monitoring, Analysis, and Reporting Technology, or S.M.A.R.T., is a monitoring system for computer hard disks to detect and report on various indicators of reliability, in the hope of anticipating failures.

Background

Fundamentally, hard drives can suffer one of two classes of failures:

• Predictable ones, when some failure modes, especially mechanical wear and aging, happen gradually over time. A monitoring device can detect these, much as a temperature dial on the dashboard of an automobile can warn a driver — before serious damage occurs — that the engine has started to overheat.
• Unpredictable ones, when other failures may occur suddenly and unpredictably, such as an electronic component burning out.

Mechanical failures, which are usually predictable failures, account for 60 percent of drive failure(source). The purpose of S.M.A.R.T. is to warn a user or system administrator of impending drive failure while time remains to take preventive action — such as copying the data to a replacement device. Approximately 30% of failures can be predicted by S.M.A.R.T.

pctechguide's page on S.M.A.R.T. (2003) comments that the technology has gone through three phases:

"In its original incarnation SMART provided failure prediction by monitoring certain online hard drive activities. A subsequent version improved failure prediction by adding an automatic off-line read scan to monitor additional operations. The latest SMART III technology not only monitors hard drive activities but adds failure prevention by attempting to detect and repair sector errors. Also, whilst earlier versions of the technology only monitored hard drive activity for data that was retrieved by the operating system, SMART III 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."

Standards and implementation

Compaq pioneered S.M.A.R.T., but most major hard-drive and motherboard vendors now support it to some extent. Many motherboards will display a warning message when a disk drive approaches failure. Although an industry standard amongst most major hard drive manufacturers, there are some remaining issues and much proprietary "secret knowledge" held by individual manufacturers as to their specific approach. As a result, S.M.A.R.T. is not always implemented correctly on many computer platforms due to the absence of industry-wide software & hardware standards for S.M.A.R.T. data interchange.

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 — thus a disk drive manufacturer could include a sensor for just one physical attribute and then advertise the product as S.M.A.R.T. compatible. For example, a drive manufacturer might claim to support S.M.A.R.T. but not include a temperature sensor, which the customer might reasonably expect to be present since reliability typically is the inverse of temperature, in which case temperature would be a crucial predictor of failure.

Some S.M.A.R.T.-enabled motherboards and related software may not communicate with certain S.M.A.R.T.-capable drives, depending on the type of interface. 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 (e.g. SCSI, Fibre Channel, ATA, SATA, SAS, SSA) it's difficult to predict whether S.M.A.R.T. reports will function correctly.

Even on hard drives and interfaces that support it, S.M.A.R.T. data may not be reported correctly to the computer's operating system. Some disk controllers can duplicate all write operations on a secondary "backup" drive in real-time. This feature is known as "RAID mirroring". However, many programs which are designed to analyze changes in drive behavior and relay S.M.A.R.T. alerts to the operator do not function when a computer system is configured for RAID support, usually because under normal RAID array operational conditions, the computer may not be permitted to 'see' (or directly access) individual physical drives, but only logical volumes, by the RAID array subsystem.

On the Windows platform, many programs designed to monitor and report S.M.A.R.T. information will only function under an administrator account. At present S.M.A.R.T. is implemented individually by manufacturers, and while some aspects are standardized for compatibility, others are not.

One of the other fundamental problems with S.M.A.R.T is that it slows performance and for this reason it is disabled by default in many motherboard BIOSes.

Attributes

Each drive manufacturer defines a set of attributes and selects threshold values which attributes should not go below under normal operation. Attribute values can range from 1 to 253 (1 representing the worst case and 253 representing the best). Depending on the manufacturer, a value of 100 or 200 will often be chosen as the "normal" value. Manufacturers that have supported one or more S.M.A.R.T. attributes in various products include: Samsung, Seagate, IBM (Hitachi), Fujitsu, Maxtor, Western Digital. These manufacturers do not necessarily agree on precise attribute definitions and measurement units; therefore the following list should be regarded as a general reference only. Note that the attribute values are always mapped to the range of 1 to 253 in a way that means higher values are better. For example, the "Reallocated Sectors Count" attribute value decreases as the number of reallocated sectors increases. In this case, the attribute's raw value will often indicate the actual number of sectors that were reallocated, although vendors are in no way required to adhere to this convention.

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

(Attributes marked "CRITICAL" are potential indicators of imminent electromechanical failure)

ID	Hex	Attribute name	Description
01	01	Read Error Rate	*CRITICAL* Indicates the rate of hardware read errors that occurred when reading data from a disk surface. Lower values indicate a problem with either disk surface or read/write heads.
02	02	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 your disk.
03	03	Spin-Up Time	Average time of spindle spin up (from zero RPM to fully operational).
04	04	Start/Stop Count	A tally of spindle start/stop cycles.
05	05	Reallocated Sectors Count	*CRITICAL* Count of reallocated sectors. When the hard drive finds a read/write/verification error, it marks this sector as "reallocated" and transfers data to a special reserved area (spare area). This process is also known as remapping and "reallocated" sectors are called remaps. This is why, on modern hard disks, you can not see "bad blocks" while testing the surface — all bad blocks are hidden in reallocated sectors. However, the more sectors that are reallocated, the more read/write speed will decrease.
06	06	Read Channel Margin	Margin of a channel while reading data. The function of this attribute is not specified.
07	07	Seek Error Rate	Rate of seek errors of the magnetic heads. If there is a failure in the mechanical positioning system, a servo damage or a thermal widening of the hard disk, seek errors arise. More seek errors indicates a worsening condition of a disk surface and the mechanical subsystem.
08	08	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.
09	09	Power-On Hours (POH)	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. A decrease of this attribute value to the critical level (threshold) indicates a decrease of the MTBF (Mean Time Between Failure). However, in reality, even if the MTBF value falls to zero, it does not mean the MTBF resource is completely exhausted and the drive will not function normally.
10	0A	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). A decrease of this attribute value is a sign of problems in the hard disk mechanical subsystem.
11	0B	Recalibration Retries	This attribute indicates the number of times recalibration was requested (under the condition that the first attempt was unsuccessful). A decrease of this attribute value is a sign of problems in the hard disk mechanical subsystem.
12	0C	Device Power Cycle Count	This attribute indicates the count of full hard disk power on/off cycles.
13	0D	Soft Read Error Rate	Uncorrected read errors reported to the operating system.
190	BE	Airflow Temperature (WDC)	Airflow temperature on Western Digital HDs (Same as temp. (C2), but current value is 50 less.)
193	C1	Load/Unload Cycle	Count of load/unload cycles into head landing zone position.
194	C2	Temperature	Current internal temperature.
195	C3	Hardware ECC Recovered	Time between ECC-corrected errors? It goes up and down, low is probably bad.
196	C4	Reallocation Event Count	*CRITICAL* Count of remap operations. The raw value of this attribute shows the total number of attempts to transfer data from reallocated sectors to a spare area. Both successful & unsuccessful attempts are counted.
197	C5	Current Pending Sector Count	*CRITICAL* Number of "unstable" sectors (waiting to be remapped). When unstable sectors are read successfully, the value is decreased. If errors occur when reading a sector, the drive will attempt to recover the data, transfer it to the reserved (spare) area and mark the sector as remapped.
198	C6	Uncorrectable Sector Count	*CRITICAL* The total number 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.
199	C7	UltraDMA CRC Error Count	The number of errors in data transfer via the interface cable as determined by ICRC (Interface Cyclic Redundancy Check).
200	C8	Write Error Rate / Multi-Zone Error Rate	The total number of errors when writing a sector.
220	DC	Disk Shift	*CRITICAL* Distance the disk has shifted relative to the spindle (usually due to shock). Unit of measure is unknown.
221	DD	G-Sense Error Rate	The number of errors resulting from externally-induced shock & vibration.
222	DE	Loaded Hours	Time spent operating under data load (movement of magnetic head armature)
223	DF	Load/Unload Retry Count	Number of times head changes position.
224	E0	Load Friction	Resistance caused by friction in mechanical parts while operating.
226	E2	Load 'In'-time	Total time of loading on the magnetic heads actuator (time not spent in parking area).
227	E3	Torque Amplification Count	Number of attempts to compensate for platter speed variations
228	E4	Power-Off Retract Cycle	The number of times the magnetic armature was retracted automatically as a result of cutting power.
230	E6	GMR Head Amplitude	Amplitude of "thrashing" (distance of repetitive forward/reverse head motion)

References

"S.M.A.R.T. attribute meaning". PalickSoft. Retrieved February 3. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

External links

• Out SMART Your Hard Drive
• How S.M.A.R.T. is your hard drive?

Software

Various operating-system specific software can extend the users ability to monitor disk drive conditions through the S.M.A.R.T. interface and predict when a failure is likely to occur by logging deviations in attribute values. This software may also possess the capability to distinguish between gradual degradation over time (representing normal wear) and a sudden change (which may indicate a more serious problem).

• S.M.A.R.T site; links to several SMART tools.
• smartmontools — open-source for Linux, FreeBSD, NetBSD, OpenBSD, Solaris, Darwin and OS/2; they also run on Windows, under the Cygwin environment.
• SMARTReporter — open-source for Apple Macintosh