SMART, aka Self-Monitoring, Analysis, and Reporting Technology, is a built-in disk drive diagnostics technology to detect and report on various indicators of reliability, in the hope of anticipating failures. It's pretty common in standard discs nowadays (the Macs I've used in the past couple of years have that feature built-in their discs).

Google, which uses millions of disc drives, has published an interesting study that shows that SMART diagnostics are not as useful as they are supposed to be. Their findings are:

- Very little correlation between failure rates and either raised temperature or activity levels. - Some SMART parameters (scan errors, reallocation counts, offline reallocation counts, and probational counts) have a large impact on failure probability. Others do not. Out of all failed drives, over 56 percent of them had no count in any of these four strong SMART signals. - There was a lack of failure-predicting SMART signals on a large proportion of failed drives. - Taking all SMART signals and temperature readings into account they found about 36 percent of all failed drives had no predictive failure signals at all.

From Techworld: It ain't smart to rely on SMART.