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.
On Mac OS X :
The following command will report the SMART status on Mac OS X
$diskutil info disk0 | grep SMART
The output will look like some thing below :
SMART Status: Verified
If the output says "Failing" or "About to Fail", other than "Verified" then you might need to backup data and try repairing the disk or replacing the disk.
On Linux :
$ smartctl -d ata -H /dev/sdb
This command will run overall-health self-assessment test on your hard disk and prints a report of disk test results.