Modern disks drives have a diagnostic on board processor that monitors the disk during operation and records various diagnostic values including any detected failures. This diagostic method, S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology; often written as SMART) is a monitoring system for computer hard disk drives to detect and report on various indicators of reliability, in the hope of anticipating failures. For more information about SMART and its values, please see http://en.wikipedia.org/wiki/S.M.A.R.T.

SMART data can be accessed and used for active testing using a SMART diagnostic program. There are numerous SMART monitoring tools available- we recommend the following:
*SMART data is only available on Macs through a SATA/eSATA connection.