Disk drive servoing on first disk surface while erasing second disk surface

1. A disk drive comprising:

a first disk surface comprising servo information;

a first head actuated over the first disk surface;

a second disk surface;

a second head actuated over the second disk surface;

a voice coil motor (VCM) operable to actuate the first and second heads radially over the respective disk surfaces; and

control circuitry operable to:

rotate the first disk surface and the second disk surface;

read the servo information from the first disk surface using the first head to generate a read signal; and

process the read signal to generate a control signal applied to the VCM to move the second head radially over the second disk surface while applying an erase signal to the second head in order to erase at least part of the second disk surface,

wherein:

the second head comprises a write element that spans a radial segment of the second disk surface;

the control circuitry is operable to move the second head radially over the second disk surface such that the write element moves less than the radial segment over a single revolution of the second disk surface; and

the radial segment changes toward a middle diameter of the second disk surface.

2. The disk drive as recited in claim 1 , wherein the servo information comprises a plurality of concentric servo sectors extending across substantially an entire radius of the first disk surface.

3. The disk drive as recited in claim 1 , wherein the control circuitry is operable to concurrently read the servo information from the first disk surface and apply the erase signal to the second head in order erase part of the second disk surface.

4. The disk drive as recited in claim 1 , wherein the erase signal comprises a direct current (DC) signal.

5. The disk drive as recited in claim 1 , wherein the erase signal comprises an alternating current (AC) signal.

6. The disk drive as recited in claim 1 , wherein the control circuitry is operable to:

move the second head radially over the second disk surface near an outer diameter at a first velocity; and

move the second head radially over the second disk surface near a middle diameter at a second velocity different than the first velocity.

7. The disk drive as recited in claim 1 , wherein the control circuitry is operable to erase a radial section of the second disk surface by moving the second head over the radial segment one time.

8. The disk drive as recited in claim 1 , wherein prior to erasing at least part of the second disk surface the control circuitry is operable to:

move the second head radially over the second disk surface while writing a spiral servo track on the second disk surface; and

after writing at least part of the spiral servo track on the second disk surface, move the second head radially over the second disk surface while applying the erase signal to the second head in order to erase at least part of the spiral servo track.

9. The disk drive as recited in claim 8 , wherein:

the second head comprises a write element that spans a radial segment of the second disk surface; and

the control circuitry is operable to move the second head radially over the second disk surface such that the write element moves more than twice the radial segment over a single revolution of the second disk surface while writing the spiral servo track.

10. The disk drive as recited in claim 9 , wherein after writing at least part of the spiral servo track on the second disk surface, the control circuitry is operable to move the second head radially over the second disk surface such that the write element moves less than the radial segment over a single revolution of the second disk surface while erasing at least part of the spiral servo track.

11. A method of operating a disk drive, the disk drive comprising a first head actuated over a first disk surface comprising servo information, a second head actuated over a second disk surface, and a voice coil motor (VCM) operable to actuate the first and second heads radially over the respective disk surfaces, the method comprising:

rotating the first disk surface and the second disk surface;

reading the servo information from the first disk surface using the first head to generate a read signal; and

processing the read signal to generate a control signal applied to the VCM to move the second head radially over the second disk surface while applying an erase signal to the second head in order to erase at least part of the second disk surface,

wherein:

the second head comprises a write element that spans a radial segment of the second disk surface;

the method further comprises moving the second head radially over the second disk surface such that the write element moves less than the radial segment over a single revolution of the second disk surface; and

the radial segment changes toward a middle diameter of the second disk surface.

12. The method as recited in claim 11 , wherein the servo information comprises a plurality of concentric servo sectors extending across substantially an entire radius of the first disk surface.

13. The method as recited in claim 11 , further comprising concurrently reading the servo information from the first disk surface and apply the erase signal to the second head in order erase part of the second disk surface.

14. The method as recited in claim 11 , wherein the erase signal comprises a direct current (DC) signal.

15. The method as recited in claim 11 , wherein the erase signal comprises an alternating current (AC) signal.

16. The method as recited in claim 11 , further comprising:

moving the second head radially over the second disk surface near an outer diameter at a first velocity; and

moving the second head radially over the second disk surface near a middle diameter at a second velocity different than the first velocity.

17. The method as recited in claim 11 , further comprising erasing a radial section of the second disk surface by moving the second head over the radial segment one time.

18. The method as recited in claim 11 , wherein prior to erasing at least part of the second disk surface the method further comprises:

moving the second head radially over the second disk surface while writing a spiral servo track on the second disk surface; and

after writing at least part of the spiral servo track on the second disk surface, moving the second head radially over the second disk surface while applying the erase signal to the second head in order to erase at least part of the spiral servo track.

19. The method as recited in claim 18 , wherein:

the second head comprises a write element that spans a radial segment of the second disk surface; and

the method further comprises moving the second head radially over the second disk surface such that the write element moves more than twice the radial segment over a single revolution of the second disk surface while writing the spiral servo track.

20. The method as recited in claim 19 , wherein after writing at least part of the spiral servo track on the second disk surface, further comprising moving the second head radially over the second disk surface such that the write element moves less than the radial segment over a single revolution of the second disk surface while erasing at least part of the spiral servo track.