Disk drive returning dummy data to a host when reading an unwritten data sector

1. A disk drive comprising:

a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors;

a head actuated over the disk; and

control circuitry operable to:

receive a read command from a host to read data from a target data sector;

determine whether the target data sector has been written in response to a write command received from the host; and

when the target data sector has not been written in response to the write command, return dummy data to the host,

wherein:

when the target data sector has been written in response to the write command, the control circuitry is further operable to return an error message to the host when the target data sector is unrecoverable; and

when the target data sector has not been written in response to the write command, the control circuitry is further operable to return the dummy data to the host when the target data sector is unrecoverable.

2. The disk drive as recited in claim 1 , wherein the dummy data comprises predetermined data.

3. The disk drive as recited in claim 2 , wherein the predetermined data comprises a plurality of zero bits.

4. The disk drive as recited in claim 1 , wherein the dummy data comprises data read from the target data sector.

5. The disk drive as recited in claim 1 , wherein when the target data sector has not been written in response to the write command, the control circuitry is further operable to write verify the target data sector when the target data sector is unrecoverable.

6. The disk drive as recited in claim 1 , wherein when the target data sector has not been written in response to the write command, the control circuitry is further operable to relocate the target data sector to a spare sector when the target data sector is unrecoverable.

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

receive the write command from the host to write user data to the target data sector; and

update a write table to reflect that the target data sector has been written in response to the write command.

8. The disk drive as recited in claim 7 , wherein:

the write table comprises a plurality of entries, wherein each entry identifies a zone corresponding to a plurality of data sectors; and

the control circuitry is operable to update an entry in the write table corresponding to the target data sector when the control circuitry writes data to any data sector in the zone comprising the target data sector.

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

write manufacturing data and a first sync mark to the target data sector during a manufacturing process;

receive the write command from the host to write user data to the target data sector, and in response to the write command write the user data and a second sync mark to the target data sector, wherein the second sync mark is different from the first sync mark; and

determining that the target data sector has been written in response to the write command by detecting the second sync mark.

10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to:

write a first preamble preceding the first sync mark to the target data sector during the manufacturing process, wherein the first preamble ends with a first phase; and

in response to the write command received from the host, write a second preamble preceding the second sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase.

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

write a first preamble and a first sync mark to the target data sector during a manufacturing process, wherein the first preamble ends with a first phase;

in response to the write command received from the host, write a second preamble and the first sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase; and

determine that the target data sector has been written in response to the write command detecting the second preamble and the first sync mark.

12. A method of operating a disk drive, the disk drive comprising a disk and a head actuated over the disk, wherein the disk comprises a plurality of tracks and each track comprises a plurality of data sectors, the method comprising:

receiving a read command from a host to read data from a target data sector;

determining whether the target data sector has been written in response to a write command received from the host; and

when the target data sector has not been written in response to the write command, returning dummy data to the host,

wherein:

when the target data sector has been written in response to the write command, further comprising returning an error message to the host when the target data sector is unrecoverable; and

when the target data sector has not been written in response to the write command, further comprising returning the dummy data to the host when the target data sector is unrecoverable.

13. The method as recited in claim 12 , wherein the dummy data comprises predetermined data.

14. The method as recited in claim 13 , wherein the predetermined data comprises a plurality of zero bits.

15. The method as recited in claim 12 , wherein the dummy data comprises data read from the target data sector.

16. The method as recited in claim 12 , wherein when the target data sector has not been written in response to the write command, further comprising write verifying the target data sector when the target data sector is unrecoverable.

17. The method as recited in claim 12 , wherein when the target data sector has not been written in response to the write command, further comprising relocating the target data sector to a spare sector when the target data sector is unrecoverable.

18. The method as recited in claim 12 , further comprising:

receiving the write command from the host to write user data to the target data sector; and

updating a write table to reflect that the target data sector has been written in response to the write command.

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

the write table comprises a plurality of entries, wherein each entry identifies a zone corresponding to a plurality of data sectors; and

updating the write table comprises updating an entry in the write table corresponding to the target data sector when data is written to any data sector in the zone comprising the target data sector.

20. The method as recited in claim 12 , further comprising:

writing manufacturing data and a first sync mark to the target data sector during a manufacturing process;

receiving the write command from the host to write user data to the target data sector, and in response to the write command writing the user data and a second sync mark to the target data sector, wherein the second sync mark is different from the first sync mark; and

determining that the target data sector has been written in response to the write command by detecting the second sync mark.

21. The method as recited in claim 20 , further comprising:

writing a first preamble preceding the first sync mark to the target data sector during the manufacturing process, wherein the first preamble ends with a first phase; and

in response to the write command received from the host, writing a second preamble preceding the second sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase.

22. The method as recited in claim 12 , further comprising:

writing a first preamble and a first sync mark to the target data sector during a manufacturing process, wherein the first preamble ends with a first phase;

in response to the write command received from the host, writing a second preamble and the first sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase; and

determining that the target data sector has been written in response to the write command by detecting the second preamble and the first sync mark.

23. A disk drive comprising:

a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors;

a head actuated over the disk; and

control circuitry operable to:

receive a read command from a host to read data from a target data sector;

determine whether the target data sector has been written in response to a write command received from the host;

when the target data sector has not been written in response to the write command, return dummy data to the host;

write manufacturing data and a first sync mark to the target data sector during a manufacturing process;

receive the write command from the host to write user data to the target data sector, and in response to the write command write the user data and a second sync mark to the target data sector, wherein the second sync mark is different from the first sync mark; and

determining that the target data sector has been written in response to the write command by detecting the second sync mark.

24. A disk drive comprising:

a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors;

a head actuated over the disk; and

control circuitry operable to:

receive a read command from a host to read data from a target data sector;

determine whether the target data sector has been written in response to a write command received from the host;

when the target data sector has not been written in response to the write command, return dummy data to the host;

write a first preamble and a first sync mark to the target data sector during a manufacturing process, wherein the first preamble ends with a first phase;

in response to the write command received from the host, write a second preamble and the first sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase; and

determine that the target data sector has been written in response to the write command by detecting the second preamble and the first sync mark.

25. A method of operating a disk drive, the disk drive comprising a disk and a head actuated over the disk, wherein the disk comprises a plurality of tracks and each track comprises a plurality of data sectors, the method comprising:

receiving a read command from a host to read data from a target data sector;

determining whether the target data sector has been written in response to a write command received from the host;

when the target data sector has not been written in response to the write command, returning dummy data to the host;

writing manufacturing data and a first sync mark to the target data sector during a manufacturing process;

receiving the write command from the host to write user data to the target data sector, and in response to the write command writing the user data and a second sync mark to the target data sector, wherein the second sync mark is different from the first sync mark; and

determining that the target data sector has been written in response to the write command by detecting the second sync mark.

26. A method of operating a disk drive, the disk drive comprising a disk and a head actuated over the disk, wherein the disk comprises a plurality of tracks and each track comprises a plurality of data sectors, the method comprising:

receiving a read command from a host to read data from a target data sector;

determining whether the target data sector has been written in response to a write command received from the host;

when the target data sector has not been written in response to the write command, returning dummy data to the host;

writing a first preamble and a first sync mark to the target data sector during a manufacturing process, wherein the first preamble ends with a first phase;

in response to the write command received from the host, writing a second preamble and the first sync mark to the target data sector, wherein the second preamble ends with a second phase different than the first phase; and

determining that the target data sector has been written in response to the write command by detecting the second preamble and the first sync mark.