Disk drive adjusting read-ahead to optimize cache memory allocation

• US 6,910,099 B1
• Filed: 09/30/2002
• Issued: 06/21/2005
• Est. Priority Date: 10/31/2001
• Status: Expired due to Fees

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Wang, Ming Y., Thelin, Gregory B.
• Primary Examiner(s): Sparks, Donald
• Assistant Examiner(s): Peugh, Brian R.
• Application Number:
  US10/262,469
• Time in Patent Office: 995 Days
• Field of Search: 711/112, 711/113, 711/133, 711/134, 711/141, 711/144, 711/145, 711/170, 711/171, 711/137, 710/52, 710/56
• US Class Current: 711/113
• CPC Class Codes: H01R 13/5213 Covers
• CPC Class Codes: H01R 13/748 using one or more screws H01R13/746 takes precedence

Abstract

A disk drive is disclosed which receives a read command from a host computer, the read command comprising a command size representing a number of blocks of read data to read from the disk. A number M of cache segments are allocated from a cache buffer, wherein each cache segment comprises N blocks. The number M of allocated cache segments is computed by summing the command size with a predetermined default number of read-ahead blocks to generate a summation, and integer dividing the summation by N leaving a residue number of default read-ahead blocks. In one embodiment, the residue number of default read-ahead blocks are not read, in another embodiment the residue number of default read-ahead blocks are read if the residue number exceeds a predetermined threshold, and in yet another embodiment the number of read-ahead blocks is extended so that the summation divides evenly by N.

Claims

1. A disk drive comprising:

(a) a disk comprising a plurality of tracks, each track comprising a plurality of blocks;

(b) a head actuated radially over the disk;

(c) a semiconductor memory comprising a cache buffer for caching data written to the disk and data read from the disk; and

(d) a disk controller for;

receiving a read command from a host computer, the read command comprising a command size representing a number of blocks of read data to read from the disk;

allocating M cache segments from the cache buffer, wherein;

each of the M cache segment comprises N blocks; and

the number M of allocated cache segments is computed by;

summing the command size with a predetermined default number of read-ahead blocks to generate a summation; and

integer dividing the summation by N which results in a residue number of default read-ahead blocks;

reading the read data from the disk and storing the read data in part of the allocated cache segments; and

adjusting a read-ahead operation in response to the residue number of default read-ahead blocks to read read-ahead data from the disk following the read data and storing the read-ahead data in a remainder of the allocated cache segments.

2. The disk drive as recited in claim 1, wherein the read-ahead operation is terminated prior to reading the residue number of default read-ahead blocks.

3. The disk drive as recited in claim 1, wherein if the residue number of default read-ahead blocks exceeds a threshold, the disk controller for:

(a) allocating an additional cache segment;

(b) reading the residue number of default read-ahead blocks from the disk; and

(c) storing the residue number of default read-ahead blocks in the additional cache segment.

4. The disk drive as recited in claim 1, wherein if the residue number of default read-ahead blocks is non-zero, the disk controller for:

(a) allocating an additional cache segment;

(b) reading the residue number of default read-ahead blocks from the disk;

(c) reading an extended number of read-ahead blocks from the disk; and

(d) storing the residue number of default read-ahead blocks and the extended number of read-ahead blocks in the additional cache segment.

5. The disk drive as recited in claim 1, wherein the number of allocated cache segments is computed by summing a predetermined number of pre-read blocks with the command size and the predetermined default number of read-ahead blocks to generate the summation.

6. The disk drive as recited in claim 1, wherein:

(a) the cache buffer comprises a plurality of cache segments each comprising P blocks where P<

N; and

(b) the disk controller for allocating the cache segments comprising P blocks for write commands.

7. The disk drive as recited in claim 6, wherein:

(a) the cache buffer comprises a plurality of segment pools;

(b) each segment pool comprises a plurality of cache segments; and

(c) each cache segment comprises 2^k number of blocks where k is a predetermined integer for each segment pool.

8. A method of reading data through a head actuated radially over a disk in a disk drive, the disk comprising a plurality of tracks, each track comprising a plurality of blocks, the disk drive comprising a cache buffer for caching read data, the method comprising the steps of:

(a) receiving a read command from a host computer, the read command comprising a command size representing a number of blocks of read data to read from the disk;

(b) allocating M cache segments of the cache buffer, wherein;

each of the M cache segments comprises N blocks; and

the number M of allocated cache segments is computed by;

summing the command size with a predetermined default number of read-ahead blocks to generate a summation; and

integer dividing the summation by N which results in a residue number of default read-ahead blocks;

(c) reading the read data from the disk and storing the read data in part of the allocated cache segments; and

(d) adjusting a read-ahead operation in response to the residue number of default read-ahead blocks to read read-ahead data from the disk following the read data and storing the read-ahead data in a remainder of the allocated cache segments.

9. The method of reading data as recited in claim 8, further comprising the step of terminating the read-ahead operation prior to reading the residue number of default read-ahead blocks.

10. The method of reading data as recited in claim 8, wherein if the residue number of default read-ahead blocks exceeds a threshold, further comprising the steps of:

(a) allocating an additional cache segment;

(b) reading the residue number of default read-ahead blocks from the disk; and

(c) storing the residue number of default read-ahead blocks in the additional cache segment.

11. The method of reading data as recited in claim 8, wherein if the residue number of default read-ahead blocks is non-zero, further comprising the steps of:

(a) allocating an additional cache segment;

(b) reading the residue number of default read-ahead blocks from the disk;

(c) reading an extended number of read-ahead blocks from the disk; and

(d) storing the residue number of default read-ahead blocks and the extended number of read-ahead blocks in the additional cache segment.

12. The method of reading data as recited in claim 8, wherein the number of allocated cache segments is computed by summing a predetermined number of pre-read blocks with the command size and the predetermined default number of read-ahead blocks to generate the summation.

13. The method of reading data as recited in claim 8, wherein the cache buffer comprises a plurality of cache segments each comprising P blocks where P<

N, further comprising the step of allocating the cache segments comprising P blocks for write commands.

14. The method of reading data as recited in claim 13, wherein:

(a) the cache buffer comprises a plurality of segment pools;

(b) each segment pool comprises a plurality of cache segments; and

(c) each cache segment comprises 2^k number of blocks where k is a predetermined integer for each segment pool.