Hard disks have a built-in health-check tool called SMART (Self-Monitoring, Analysis, and Reporting Technology), which continually checks the disk for potential problems. SMART also warns you if the disk is about to fail, helping you avoid loss of important data.
Although SMART runs automatically, you can also check your disk's health by running the Disk Utility application:
Open the Disk Utility application from the Activities overview.
Select the disk you want to check from the Storage Devices list. Information and status of the disk will appear under Drive.
SMART Status should say "Disk is healthy".
Click the SMART Data button to view more drive information, or to run a self-test.
Even if the SMART Status indicates that the disk isn't healthy, there may be no cause for alarm. However, it's better to be prepared with a to prevent data loss.
If the status says "Pre-fail", the disk is still reasonably healthy but signs of wear have been detected which mean it might fail in the near future. If your hard disk (or computer) is a few years old, you are likely to see this message on at least some of the health checks. You shouldand check the disk status periodically to see if it gets worse.
If it gets worse, you may wish to take the computer/hard disk to a professional for further diagnosis or repair.