Disk drive servoing off of first head while determining fly height for second head

1. A method of selecting a dynamic fly height (DFH) control setting for a head in a disk drive, the disk drive comprising a plurality of disk surfaces and plurality of respective heads, the method comprising:

servoing a first head over a first disk surface in response to servo data recorded on the first disk surface;

adjusting a first DFH control setting for a second head; and

while servoing the first head over the first disk surface, detecting whether the second head has contacted a second disk surface.

2. The method as recited in claim 1 , further comprising selecting an operating DFH control setting for the second head in response to the adjusted first DFH control setting.

3. The method as recited in claim 2 , further comprising:

adjusting a second DFH control setting for a third head; and

while servoing the first head over the first disk surface, detecting whether the third head has contacted a third disk surface.

4. The method as recited in claim 3 , further comprising selecting an operating DFH control setting for the second head and an operating DFH control setting for the third head in response to the adjusted first DFH control setting and the adjusted second DFH control setting.

5. The method as recited in claim 4 , further comprising bank servo writing the second and third disk surfaces using the operating DFH control settings for the second and third heads.

6. The method as recited in claim 2 , wherein selecting the operating DFH control setting for the second head comprises:

selecting a digital-to-analog setting for generating a first signal; and

selecting a scalar setting for amplifying the first signal.

7. The method as recited in claim 3 , wherein:

adjusting the first DFH control setting for the second head comprises adjusting a digital-to-analog setting for generating a first signal; and

adjusting the second DFH control setting for the third head comprises adjusting the digital-to-analog setting for generating a second signal.

8. The method as recited in claim 7 , further comprising:

selecting a first scalar setting for amplifying the first signal;

selecting a second scalar setting for amplifying the second signal; and

selecting a global digital-to-analog setting in response to the adjusted first DFH control setting, the adjusted second DFH control setting, the first scalar setting, and the second scalar setting.

9. The method as recited in claim 8 , wherein selecting the global digital-to-analog setting comprises minimizing an equation:

∑

i

=

1

N

⁢

(

GL

i

-

P

i

)

2

where:

N is a total number of heads in the disk drive;

G is the global digital-to-analog setting;

P i is the adjusted DFH control setting for the i th head; and

L i is the scalar setting for the i th head.

10. The method as recited in claim 1 , wherein the servo data comprises a plurality of spiral tracks recorded on the first disk surface.

11. A disk drive comprising:

a plurality of disk surfaces;

a plurality of heads actuated over the respective disk surfaces; and

control circuitry operable to select a dynamic fly height (DFH) control setting for a second head by:

servoing a first head over a first disk surface in response to servo data recorded on the first disk surface;

adjusting a first DFH control setting for the second head; and

while servoing the first head over the first disk surface, detecting whether the second head has contacted a second disk surface.

12. The disk drive as recited in claim 11 , wherein the control circuitry is further operable to select an operating DFH control setting for the second head in response to the adjusted first DFH control setting.

13. The disk drive as recited in claim 12 , wherein the control circuitry is further operable to:

adjust a second DFH control setting for a third head; and

while servoing the first head over the first disk surface, detect whether the third head has contacted a third disk surface.

14. The disk drive as recited in claim 13 , wherein the control circuitry is further operable to select an operating DFH control setting for the second head and an operating DFH control setting for the third head in response to the adjusted first DFH control setting and the adjusted second DFH control setting.

15. The disk drive as recited in claim 14 , wherein the control circuitry is further operable to bank servo write the second and third disk surfaces using the operating DFH control settings for the second and third heads.

16. The disk drive as recited in claim 12 , wherein selecting the operating DFH control setting for the second head comprises:

selecting a digital-to-analog setting for generating a first signal; and

selecting a scalar setting for amplifying the first signal.

17. The disk drive as recited in claim 13 , wherein:

adjusting the first DFH control setting for the second head comprises adjusting a digital-to-analog setting for generating a first signal; and

adjusting the second DFH control setting for the third head comprises adjusting the digital-to-analog setting for generating a second signal.

18. The disk drive as recited in claim 17 , wherein the control circuitry is further operable to:

select a first scalar setting for amplifying the first signal;

select a second scalar setting for amplifying the second signal; and

select a global digital-to-analog setting in response to the adjusted first DFH control setting, the adjusted second DFH control setting, the first scalar setting, and the second scalar setting.

19. The disk drive as recited in claim 18 , wherein selecting the global digital-to-analog setting comprises minimizing an equation:

∑

i

=

1

N

⁢

(

GL

i

-

P

i

)

2

where:

N is a total number of heads in the disk drive;

G is the global digital-to-analog setting;

P i is the adjusted DFH control setting for the i th head; and

L i is the scalar setting for the i th head.

20. The disk drive as recited in claim 11 , wherein the servo data comprises a plurality of spiral tracks recorded on the first disk surface.

21. A disk drive comprising:

a plurality of disk surfaces;

a plurality of heads actuated over the respective disk surfaces; and

control circuitry operable to select a global digital-to-analog setting for the plurality of heads by:

adjusting a first digital-to-analog setting for a first head to generate a first signal;

adjusting a second digital-to-analog setting for a second head to generate a second signal;

selecting a first scalar setting for scaling the first signal;

selecting a second scalar setting for scaling the second signal; and

selecting the global digital-to-analog setting in response to the adjusted first digital-to-analog setting, the adjusted second digital-to-analog setting, the first scalar setting, and the second scalar setting, wherein the global digital-to-analog setting comprises a dynamic fly height (DFH) control setting.