A method and apparatus for detecting flaws requiring sparing of portions of storage media included as part of a hard disk drive are provided. A window of a selected portion of the storage medium is formed, and the density of defects detected within that window is calculated. If the density of defects exceeds a threshold amount, a signal is passed to the controller. The portion of the storage media containing the defects that caused the generation of the flag may then be spared. The present invention allows the potential for detected defects to significantly affect the ability of the storage medium to be assessed. Furthermore, the present invention does not require that the location of each defect be stored in memory. Accordingly, the present invention is economical to implement, and allows defects to be assessed in substantially real time and with improved accuracy.