Disk drive performing spiral scan of disk surface to detect residual data

1. A disk drive comprising:

a disk surface comprising a radius;

a head operable to generate a read signal;

a voice coil motor (VCM) operable to actuate the head over the disk surface; and

control circuitry operable to:

measure a back electromotive force (BEMF) voltage generated by the VCM;

control the VCM to move the head over substantially the entire radius of the disk surface in response to the BEMF voltage; and

while moving the head, process the read signal from the head to detect residual data recorded on the disk surface after erasing the disk surface.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to process the read signal to detect the residual data recorded on the disk surface at substantially any point during the moving.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to move the head over substantially the entire radius of the disk surface a number of times, wherein each time the control circuitry is operable to start the moving from a different circumferential phase offset.

4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to move the head from a first location near an inner diameter of the disk surface until the head contacts a ramp near an outer diameter of the disk surface.

5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to calibrate a gain of a BEMF detector operable to measure the BEMF voltage of the VCM.

6. The disk drive as recited in claim 1 , further comprising a spindle motor operable to rotate the disk surface, wherein the control circuitry is further operable to:

synchronize a disk locked clock (DLC) to a rotation frequency of the disk surface; and

sample the read signal in response to the DLC to generate signal samples.

7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to filter the signal samples based on a frequency corresponding to an expected frequency of the residual data.

8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to filter the signal samples based on a number of target frequencies, wherein each target frequency corresponds to a corresponding type of residual data.

9. The disk drive as recited in claim 8 , wherein the type of residual data comprises a residual spiral servo track.

10. The disk drive as recited in claim 8 , wherein the type of residual data comprises a residual concentric servo track.

11. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to log a location of the detected residual data.

12. A method of operating a disk drive comprising a disk surface comprising a radius, a head operable to generate a read signal, and a voice coil motor (VCM) operable to actuate the head over the disk surface, the method comprising:

measuring a back electromotive force (BEMF) voltage generated by the VCM;

controlling the VCM to move the head over substantially the entire radius of the disk surface in response to the BEMF voltage; and

while moving the head, processing the read signal from the head to detect residual data recorded on the disk surface after erasing the disk surface.

13. The method as recited in claim 12 , further comprising processing the read signal to detect the residual data recorded on the disk surface at substantially any point during the moving.

14. The method as recited in claim 12 , further comprising moving the head over substantially the entire radius of the disk surface a number of times, wherein each time starting the moving from a different circumferential phase offset.

15. The method as recited in claim 12 , further comprising moving the head from a first location near an inner diameter of the disk surface until the head contacts a ramp near an outer diameter of the disk surface.

16. The method as recited in claim 12 , further comprising calibrating a gain of a BEMF detector operable to measure the BEMF voltage of the VCM.

17. The method as recited in claim 12 , further comprising a spindle motor operable to rotate the disk surface, the method further comprising:

synchronizing a disk locked clock (DLC) to a rotation frequency of the disk surface; and

sampling the read signal in response to the DLC to generate signal samples.

18. The method as recited in claim 17 , further comprising filtering the signal samples based on a frequency corresponding to an expected frequency of the residual data.

19. The method as recited in claim 18 , further comprising filtering the signal samples based on a number of target frequencies, wherein each target frequency corresponds to a corresponding type of residual data.

20. The method as recited in claim 19 , wherein the type of residual data comprises a residual spiral servo track.

21. The method as recited in claim 19 , wherein the type of residual data comprises a residual concentric servo track.

22. The method as recited in claim 12 , further comprising logging a location of the detected residual data.