S.M.A.R.T. is a Self-Monitoring, Analysis and Reporting Technology. Through the S.M.A.R.T. system, hard disk drives incorporate a suite of advanced diagnostics that monitor the internal operations of a drive and provide an early warning for many types of potential problems. When a potential problem is detected, the drive can be repaired or replaced before any data are lost.

The S.M.A.R.T. system consists of software that resides both on the disk drive and on the host computer. The software on the disk drive allows a disk drive to report data about its activity, such as the number of hours it has been in operation, the number of seek errors that have occurred and been corrected, it monitors the internal performance of the motors, media, heads, and electronics of the drive. The host software determines the overall reliability of the drive by analyzing the drive's internal performance parameters and comparing them to predetermined threshold limits.

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S.M.A.R.T. monitors a number of factors that relate to predictable drive failures. There are also unpredictable drive failures, but those we can't really do much about. Predictable failures occur as a result of bearing failure, cracked or broken read/write head, electronics module failure, changes in spin-up rate, etc. There are also factors related to the failure of the read/write surface, such as seek error rate, excessive bad sectors, and reallocated sector count. Most of these are factors that can be monitored. Then, when a threshold level is exceeded, a failure warning is transmitted. Active SMART monitors these parameters, calculates the date of the fault, and warn the user of the impending risk of a data loss and advise the user of appropriate action. S.M.A.R.T. is an industry standard reliability prediction indicator for both IDE/ATA and SCSI drives.

A drive that is S.M.A.R.T. compliant has a series of parameters (attributes) embedded on the disk drive. The data (attribute values) is constantly collected and monitored for variations within vendor specific thresholds. These tests are designed to predict the impending degradation or failure of a drive. Predictable failures are characterized by degradation of an attribute over time, before the disc drive fails. This creates a situation where attributes can be monitored, making it possible for predictive-failure analysis. Many mechanical failures are typically considered predictable, such as the degradation of head-flying height, which would indicate a potential head crash. Certain electronic failures may show degradation before failing, but more commonly, mechanical problems are gradual and predictable. For instance, oil level is a function, or “attribute” of most cars that can be monitored. When a car’s diagnostic system senses that the oil is low, an oil light comes on. In the same manner, S.M.A.R.T. allows notice to start the backup procedure and save the user’s data.
Mechanical failures, which are mainly predictable failures, account for 60 percent of drive failure. This number is significant because it demonstrates a great opportunity for reliability-prediction technology. With the emerging technology of S.M.A.R.T., an increasing number of predictable failures will be predicted, and data loss will be avoided.

But remember, that S.M.A.R.T. should be treated as an advisory service, and not a substitute for regularly backing-up your files. Keeping your data safe can only be ensured by making back-up copies on a regular basis. The S.M.A.R.T. features of any device should not be considered a substitute for planning-ahead.