S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology; often written as SMART) is a monitoring system included in computer hard disk drives (HDDs), solid-state drives (SSDs), and eMMC drives. 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 preventative action can be taken to prevent data loss, and the failing drive can be replaced and data integrity maintained.
Hard disk failures (and Flash drive failures, but not exactly in the same way) fall into one of two basic failure classes:
- Predictable failures, resulting from slow processes such as mechanical wear and gradual degradation of storage surfaces (or individual flash chips in SSDs which degrade slowly with every write operation). Monitoring can determine when such failures are becoming more likely.
- Unpredictable failures, happening without warning and ranging from electronic components becoming defective to a sudden mechanical failure (which may be related to improper handling).
Mechanical failures account for about 60% of all drive failures. 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.