To positively prevent data from recovery; disks can be removed from disk drives and broken up, or even ground to microscopic pieces. DoD 5220.22M recommends degaussing followed by physical destruction of the storage medium (the magnetic disks) for data classified higher than Secret. Even such physical destruction is not absolute if any remaining disk pieces are larger than a single 512-byte record block in size, about 1/125” in today’s drives. As linear and track densities increases, the maximum allowable size of disk fragments become ever smaller. Destroyed disk fragments of this size can be image restored by magnetic microscopy.
Some storage products are more easily destroyed than hard disk drives, such as magnetic disk data cartridges, tape cartridges, secure USB drives, and optical media.