US 6,910,099 B1Granted

Disk drive adjusting read-ahead to optimize cache memory allocation

AssigneeWestern Digital Technologies, Inc.

InventorsMing Y. Wang, Gregory B. Thelin

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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.

Claims14

Dependent claims

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.

13 more elements

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.

8 more elements

Dependencies are inferred from the claim text.