Every time you start up the SoftRAID application, it gets the SMART status* of every disk which support SMART. In addition, the SoftRAID Monitor gets the SMART status every time you restart your Mac and every 24 hours after that. Each time SoftRAID gets the SMART status of a disk, it checks to see if the disk has failed the SMART test. In addition, the SMART measurements are also used to predict whether the disk is more likely to fail. This prediction is based on results of a study by Google engineers of disk failure using 100,000 disks over an 8 month period.
*SMART is a monitoring system in disk drives that SoftRAID Monitor uses to assess drive reliability and anticipate drive failures.