Interrupting disc write operations to service read commands

1. A method for servicing read commands in a disc drive, comprising steps of:

(a) receiving in the disc drive a read command requesting data;

(b) determining that a disc write operation is in progress in the disc drive; and

(c) discontinuing the disc write operation to service the read command, wherein the discontinuing step (c) comprises step of:

(c)(1) determining if the disc write operation is to be aborted, wherein the determining step (c)(1) comprises steps of:

(c)(1)(a) determining a time (TR) required to complete the disc write operation and to access the data requested in the read command;

(c)(1)(b) comparing TR with a specified time period (TS); and

(c)(1)(c) if TR is greater than TS, determining that the write operation is to be aborted; and

(c)(2) if it is determined that the disc write operation is to be aborted, interrupting the disc write operation to service the read command.

2. A method as defined in claim 1 , wherein the disc write operation comprises writing data read from a write cache of the disc drive to data sectors on a disc of the disc drive.

3. A method as defined in claim 2 , wherein the step

(c)(1)(b) further comprises determining a value of TS corresponding to an optimal point during the disc write operation to interrupt the disc write operation; and

the step (c)(2) further comprising interrupting the disc write operation at the optimal point.

4. A method as defined in claim 3 , wherein the optimal point comprises a specified data sector of the disc drive.

5. A method as defined in claim 3 , wherein the optimal point comprises a specified servo sector of the disc drive.

6. A method as defined in claim 3 , wherein the determining step (c)(1) further comprises using a rotationally optimized seek initiation (ROSI) algorithm to determine the optimal point during the disc write operation to interrupt the disc write operation.

7. A disc drive comprising:

a disc on which data associated with a disc write operation are written and from which data associated with a read command are read; and

a write discontinuation means in the disc drive for discontinuing a disc write operation in progress in the disc drive to service a read command, wherein the write discontinuation means is operable to determine an optimal point at which to discontinue the disc write operation to service the read command.

8. A disc drive as defined in claim 7 wherein the optimal point comprises a data sector on the disc of the disc drive.

9. A disc drive as defined in claim 7 , wherein the optimal point comprises a servo sector on the disc of the disc drive.

10. A disc drive as defined in claim 7 , wherein discontinuing the disc write operation comprises aborting the disc write operation.

11. A disc drive as defined in claim 7 , wherein discontinuing the disc write operation comprises interrupting the disc write operation.

12. A disc drive as defined in claim 7 , wherein the disc drive further comprises a write cache in which data associated with the disc write operation are stored prior to being written to the disc.

13. A disc drive as defined in claim 12 , wherein the write discontinuation means further comprises means for reestablishing in the write cache data associated with the disc write operation that was not written to the disc due to the discontinuation of the disc write operation.

14. A disc drive as defined in claim 12 , wherein the write discontinuation means determines an optimal point at which to discontinue the disc write operation using a rotationally optimized seek initiation (ROSI) algorithm.

15. A disc drive as defined in claim 12 , wherein the write discontinuation means determines a time (T 1 ) required to complete the disc write operation and to access a predetermined location on the disc associated with the read command, is operable to determine a time (T 2 ) required to access the predetermined location on the disc without completing the disc write operation, and is operable to determine an optimal point at which to discontinue the disc write operation using T 1 and T 2 .

16. A disc drive as defined in claim 7 , wherein the disc drive further comprises a control means executing computer executable code for controlling the operation of the disc drive and wherein the write discontinuation means comprises computer executable code executed by the control means.

17. A system comprising:

a cache coupled to a communication channel to receive and store data until the data is transferred to a data storage medium;

a processor coupled to the cache; and

a memory for storing program instructions that, when executed by the processor, cause the processor to perform operations to process pending commands associated with data stored in the cache, the operations comprising:

initiate a first operation to service a pending first command to transfer data that is stored in the cache;

determine an optimum point at which to service the second command if a second command of higher priority than the pending first command is received while the first operation is executing; and

interrupt the first operation at or before the optimum point.

18. The system of claim 17 , wherein the operation to determine the optimum point comprises:

use a rotationally optimized seek initiation (ROSI) algorithm to determine the optimum point during the pending first operation to service the pending second command.

19. The system of claim 17 , wherein the first operation is a write operation to store data that is stored in the cache to a data storage medium, and the first command is a write command that is associated with the write operation.

20. The system of claim 19 wherein the second command is a read command that is associated with a read operation to receive data that is stored on a data storage medium.

21. The system of claim 20 , wherein the operations further comprise:

when the read command is no longer pending, resume the interrupted write operation by writing data stored in the cache that has not yet been written to a data storage medium.

22. The system of claim 20 , wherein the operation to determine the optimum point comprises:

1) calculate a time (T 1 ) indicative of the time required to service the read command if the write operation is completed before servicing the read command; and

2) calculate a time (T 2 ) indicative of the time required to service the read command if the write operation is interrupted to service the read command, wherein the time required to service the read command includes an estimate of the time required for a read transducer to be positioned to read the first sector of data associated with the pending read command.

23. The system of claim 22 , wherein the optimum point at which to interrupt the pending read command is determined as a function of T 1 and T 2 .

24. The system of claim 17 , wherein the data storage medium comprises one or more discs in a disc drive.

25. The system of claim 17 , wherein the memory for storing program instructions comprises non-volatile memory.