1. A method of operating a hard disk drive (HDD) on the basis of a predicted new defect in a disk associated with the HDD, the method comprising: detecting defects in a magnetic surface of the disk; defining a plurality of clusters by grouping the detected defects using a hierarchical clustering algorithm; calculating a curve fit for each one of the plurality of clusters; predicting a new defect likely to occur in the magnetic surface of the disk on the basis of the calculated curve fit; and writing data to the disk on the basis of the new defect prediction.