Calibrating a defect scan parameter for a disk drive

A disk drive comprising:

• a disk comprising a first data area substantially free from defects and a second data area substantially affected by at least one defect;
• a head actuated over the disk;
• and
• control circuitry operable to:
• (a) initialize a defect scan parameter with an initial setting;
• (b) read the first data area to determine a first defect threshold, and read the second data area to determine a second defect threshold;
• (c) save a margin representing a difference between the first and second defect thresholds;
• (d) adjust the setting for the defect scan parameter;
• (e) repeat (b) and (c) at least once;
• and
• (f) select a first setting for the defect scan parameter in response to the margins saved at element (c).

A disk drive comprising:

• a disk comprising a first area substantially free from defects and a second data area substantially affected by at least one defect;
• a head actuated over the disk;
• a means for sweeping through a plurality of defect scan parameter values and for reading the first and second data areas to determine a plurality of first and second defect thresholds;
• a means for determining a plurality of margins representing a difference between the first and second defect thresholds;
• and
• a means for selecting a setting for the defect scan parameter in response to the plurality of margins.