Methods and devices for enhanced adaptive margining based on channel threshold measure

1. A disk drive to enable defect margining during disk testing, comprising:

a processor operable to:

test media of the disk drive to detect a media defect;

estimate a depth of the detected media defect;

determine a margining amount based on at least the estimated depth of the detected media defect; and

apply the determined margining amount to the detected media defect.

2. The disk drive of claim 1 , wherein the margining amount is further based on a length of the detected media defect.

3. The disk drive of claim 2 , wherein a portion of the determined margining amount attributable to the length of the detected media defect is half of the length of the detected media defect as measured in tracks, plus 1 track.

4. The disk drive of claim 1 , wherein the margining amount is further based on a detected presence of a thermal asperity within the detected media defect.

5. The disk drive of claim 4 , wherein a portion of the determined margining amount attributable to the detected presence of the thermal asperity is a product of a scaling factor and a length of the detected media defect.

6. The disk drive of claim 1 , wherein the processor is further operable to apply at least a portion of the determined margining amount to at least one of an end of the detected media defect directed toward an inner diameter (ID) of the media and to an end of the detected media defect directed toward the outer diameter (OD) of the media.

7. The disk drive of claim 1 , wherein the processor is further operable to estimate the depth of the detected media defect by reading; back a signal written to the media and reducing a threshold of detection from a nominal threshold until the read back signal is no longer detectable.

8. The disk drive of claim 1 , wherein the processor is further operable to determine whether an estimated greatest depth of the detected media defect is toward an inner diameter (ID) of the media or an outer diameter (OD) of the media.

9. The disk drive of claim 8 , wherein the processor is further operable to:

apply more of the margining amount at an ID end of the media if the estimated greatest depth of the detected media defect is closer to the ID than the OD of the media; and

apply more of the margining amount at an OD end of the media if the estimated greatest depth of the detected media defect is closer to the OD than the ID of the media.

10. The disk drive of claim 8 , wherein the processor is further operable to:

select a predetermined number of reference points on the detected media defect ranging from an OD end to an ID end of the detected media defect;

estimate a local depth of the detected media defect at each of the predetermined number of reference points; and

vary the margining amount applied to at least one of the ID end and the OD end of the detected media defect based on the estimated local depth of the detected media defect at each of the predetermined number of reference points.

11. The disk drive of claim 1 , wherein a portion of the determined margining amount attributable to the estimated depth of the detected media defect comprises a calculated ratio of: (1) a product of a length of the detected media defect and the estimated depth to (2) a sum of the length of the detected media defect and the estimated depth.

12. A method to enable defect margining during testing of a disk drive, comprising:

testing media of the disk drive to detect a media defect;

estimating a depth of the detected media defect;

determining a margining amount based on at least estimated depth of the detected media defect; and

applying the determined margining amount to the detected media defect.

13. The method of claim 12 , wherein the margining amount is further based on a length of the detected media defect.

14. The method of claim 13 , wherein a portion of the determined margining amount attributable to the length of the detected media defect is half of the length of the detected media defect as measured in tracks, plus 1 track.

15. The method of claim 12 , wherein the margining amount further based on a detected presence of a thermal asperity within the detected media defect.

16. The method of claim 15 , wherein a portion of the determined margining amount attributable to the detected presence of thermal asperity is a product of a scaling factor and a length of the detected media defect.

17. The method of claim 16 , wherein applying the determined margining amount comprises applying at least a portion of the determined margining amount to at least one of an end of the detected media defect directed toward an inner diameter (ID) of the media and to an end of the detected media defect directed toward the outer diameter (OD) of the media.

18. The method of claim 12 , wherein estimating the depth of the detected media defect comprises reading back a signal written to the media and reducing a threshold of detection from a nominal threshold until the read back signal is no longer detectable.

19. The method of claim 12 , further comprising determining whether an estimated greatest depth of the detected media defect is toward an inner diameter (ID) of the media or an outer diameter (OD) of the media.

20. The method of claim 19 , further comprising:

applying more of the margining amount at an ID end of the detected media defect if the estimated greatest depth of the detected media defect is closer to the ID than the OD of the media; and

applying more of the margining amount at an OD end of the detected media defect if the estimated greatest depth of the detected media defect is closer to the OD than the ID of the media.

21. The method of claim 19 , further comprising:

selecting a predetermined number of reference points on the detected media defect ranging from an OD end to an ID end of the detected media defect;

estimating a local depth of the detected media defect at each of the predetermined number of reference points; and

varying the margining amount applied to at least one of the ID end and the OD end of the detected media defect based on the estimated local depth of the detected media defect at each of the predetermined number of reference points.

22. The method of claim 12 , wherein determining the margining amount comprises at least calculating a ratio of (1) a product of a length of the detected media defect and the estimated depth to (2) a sum of the length of the detected media defect and the estimated depth.

23. A method to enable defect margining during testing of a disk drive, comprising:

testing media of the disk drive to detect a media defect;

estimating a depth of the detected media defect;

determining a margining amount based on at least one of the estimated depth, an estimated length, and a detected thermal asperity of the detected media defect, and

applying the determined margining amount to the detected media defect.

24. The method of claim 23 , wherein the margining amount is determined based at least on the estimated length of the detected media defect and wherein a portion of the determined margining amount attributable to the estimated length of the detected media defect is half of the estimated length of the detected media defect as measured in tracks, plus 1 track.

25. The method of claim 23 , wherein the margining amount is determined based at least on the detected thermal asperity and the estimated length of the detected media defect and wherein a portion of the determined margining amount attributable to the detected thermal asperity is a product of a scaling factor and the estimated length of the detected media defect.

26. The method of claim 23 , wherein applying the determined margining amount comprises applying at least a portion of the determined margining amount to at least one of an end of the detected media defect directed toward an inner diameter (ID) of the media and to an end of the detected media defect directed toward the outer diameter (OD) of the media.

27. The method of claim 23 , wherein estimating the depth of the detected media defect comprises reading back a signal written to the media and reducing a threshold of detection from a nominal threshold until the read back signal is no longer detectable.

28. The method of claim 23 , further comprising determining whether an estimated greatest depth of the detected media defect is toward an inner diameter (ID) of the media or an outer diameter (OD) of the media.

29. The method of claim 28 , further comprising:

applying more of the margining amount at an ID end of the detected media defect if the estimated greatest depth of the detected media defect is closer to the ID than the OD of the media; and

applying more of the margining amount at an OD end of the detected media defect if the estimated greatest depth of the detected media defect is closer to the OD than the ID of the media.

30. The method of claim 28 , further comprising:

selecting a predetermined number of reference points on the detected media defect ranging from an OD end to an ID end of the detected media defect:

estimating a local depth of the detected media defect at each of the predetermined number of reference points; and

varying the margining amount applied to at least one of the ID end and the OD end of the detected media defect based on the estimated local depth of the detected media defect at each of the predetermined number of reference points.

31. The method of claim 28 , wherein determining the margining amount comprises at least calculating a ratio of: (1) a product of a length of the detected media defect and the estimated depth to (2) a sum of the length of the detected media defect and the estimated depth.