Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2002-03-20
2004-10-12
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S112000
Reexamination Certificate
active
06804751
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the data processing field, and, more particularly, relates to promoting efficient operation of a hard disk drive.
BACKGROUND OF THE INVENTION
In a hard disk drive, data signals are read from and written to a rotating disk by a head which is moved substantially radially with respect to the disk.
FIG. 1
is a simplified block diagram that illustrates conventional circuitry which controls the positioning of a head in a disk drive. Signal conditioning and reading circuitry
10
receives an input signal from arm electronics, which are not shown. A signal output from the signal conditioning and reading circuitry
10
is provided to a head control circuit
12
. The head control circuit
12
processes the signal received from the signal conditioning and reading circuitry
10
and outputs a control signal to an actuator drive circuit
14
. The actuator drive circuit
14
provides a driving signal to a head actuator motor (not shown) which typically is a voice coil motor.
The head control circuit
12
also receives commands from a host system, which is not shown. The head control circuit
12
includes a processing capability
16
, which may include one or more processors. Also included in the head control circuit
12
are one or more memory units, represented by memory block
18
in FIG.
1
.
The head control circuit
12
responds to commands from the host by moving the head from a current position to a target position. Such operations are referred to as “seeks”, and are intended to bring the head into a stable position at a target track or cylinder.
According to conventional practices, commands from the host may be queued in the head control circuit
12
, and may be selected from the queue for execution in accordance with a process intended to minimize the average access time for execution of commands. According to a known command queue ordering technique, a Shortest Access Time First (SATF) algorithm is employed. According to this algorithm, the command selected for execution from the command queue is that which can be started first. Estimated access times for commands are contained in a seek profile table stored in the memory
18
. The estimated access times indicated by the seek profile table take two factors into account: (a) the time required to seek to and settle at the target track, and (b) the additional time required for the disk to rotate so that the target sector reaches the locus of the head. This additional rotational time is sometimes referred to as “extra latency”.
When a command fails to be executed within the estimated access time indicated by the seek profile table, execution of the command must await an additional rotation of the disk. This phenomenon can degrade the performance of the disk drive, and is referred to as a “miss”.
FIG. 2
is a time line that illustrates a sequence of events which may occur in connection with a conventional manner of operating a hard disk drive. It should be noted that the time line of
FIG. 2
indicates event sequence only, and is not drawn to scale. As indicated at
20
in
FIG. 2
, the disk drive sends a status message to the host system to indicate completion of execution of an access command (i.e., a read or a write). Then the disk drive begins execution of the next access command, by starting a seek operation, as indicated at
22
. During the seek operation a new command is received at the disk drive from the host system, as indicated at
24
. The new access command is added to the command queue, and the head control circuit
12
(
FIG. 1
) proceeds to sort the command queue, as indicated at
26
, to determine which command in the queue will have the shortest access time upon completion of the execution of the command which is currently in progress. The command in the command queue which is determined to have the shortest access time is selected to be the next command to be executed after the currently executing command.
After the command queue sorting has occurred in background during the seek operation, the seek operation ends, as indicated at
28
. That is, the read/write head has reached and settled on the target track. The head then remains positioned at the target track while waiting for the disk to rotate to bring the target sector to the locus of the head. This period of waiting may be referred to as “on-track time” and is indicated at
30
. When the target sector arrives at the head, the “data phase” (indicated at
32
) occurs. That is, reading of data from the disk or writing of data to the disk takes place. Upon completion of the read or write, the disk drive sends a status message (indicated at
34
) to the host system. The cycle of operation is then repeated with respect to the next access command to be executed, which was selected during the command queue sorting operation indicated at
26
.
There may be a number of variations in the conventional sequence of events illustrated in FIG.
2
. For example, no new command may arrive prior to the command queue sort operation. Alternatively, the command queue sort operation may occur immediately after the seek start
22
, then a new command may arrive, and the command queue sort operation may be performed again to determine whether the newly arrived command has a shorter access time than the command selected at the initial sort operation. Arrival of a new command and resorting of the command queue may occur at any time during the period from seek start to completion of command execution (completion of the data phase). More than one new command may be received during this period, and consequently more than one re-sort of the command queue may occur during this period.
The conventional SATF sort operation referred to in connection with
FIG. 2
may be modified according to an invention that is commonly assigned herewith and referred to as DEAT (Delta Expected Access Time). The DEAT SATF algorithm is disclosed in co-pending commonly-assigned patent application Ser. No. 09/638,253, filed Aug. 14, 2000 (Attorney Docket Number ROC9-2000-0161-US1). This co-pending patent application is incorporated herein by reference.
In selecting a command for execution from the command queue, the DEAT SATF algorithm considers not only the estimated access time indicated by the seek profile table, but also the probability that the command will be executed within the estimated time. The probability information may be based on actual experience in executing commands, as indicated by a probability table. An example of a probability table provided according to the DEAT SATF algorithm is shown in FIG.
3
. The probability table of
FIG. 3
indicates execution experience for executed commands that have been categorized according to seek distance and estimated extra latency. The seek distance is measured in terms of cylinder groups, and the estimated extra latency is measured in terms of servo ID's. For each category of commands, the corresponding data cell indicates the “miss rate”, i.e. the percentage of executed commands in the category that have resulted in “misses”. The execution experience data provided in a miss rate table like
FIG. 3
may be used in accordance with the DEAT SATF algorithm to provide a modified estimated access time for each command in the command queue, thereby leading to improved selection of the next command for execution, by reducing the likelihood that a miss will occur during the execution of the selected command.
The present inventors have recognized that the extra latency or “on-track time” represented at
30
in the time line of
FIG. 2
may present an opportunity for still further improvements in the efficiency of operation of a disk drive.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a method of operating a disk drive is provided. The inventive method according to this aspect of the invention includes maintaining a command queue that includes a plurality of access commands that are awaiting execution, and sorting the command queue to provisionally select one of the plur
Espeseth Adam Michael
Hall David Robison
Shipman James R.
Dugan & Dugan PC
Duncan Patrick
Hitachi Global Storage Technologies - Netherlands B.V.
Kim Matthew
Patel H. B.
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