The new disks coming in market are S.M.A.R.T. ( Self-Monitoring, Analysis and Reporting Technology ) enabled. It monitors your disk and alerts you if the disk is about to fail , helpful to prevent data loss. There are many factors you find in SMART array :-
Some of them are as follows :
Read Error Rate => Lower the value good it is.
Reallocated Sectors Count => Lower the value good it is.
Reported Uncorrectable Errors => Lower the value good it is.
Current Pending Sector Count => Lower the value good it is.
and many more.
Tools to monitor and easily generate the report, prefer to use your vendor tool, or else you can use :
Ubuntu : GSmart
Windows : HD Tune
In case, if you lost your data, try spinrite, it may recover it.