Disk Drive RPO Algorithm Offset for Limited Stroke Throughput
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Solution Overview
Problem
Limited stroke disk drives face performance disparities compared to full stroke disk drives due to non-linear seek time relationships and varying servo system parameters, leading to suboptimal throughput across different command queue depths.
Innovation Solution
Increasing access latency for each access command based on a non-linear function of seek length, allowing the RPO algorithm to adjust the execution order and match the performance of full stroke disk drives by compensating for limited radial movement, either virtually or by modifying seek and rotational latencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the RPO algorithm uses standard access latency estimation, then command selection is simple and fast, but throughput performance deteriorates in limited stroke disk drives
Solution Approach 1:
The patent modifies the access latency parameter used by the RPO algorithm by adding a seek-length-dependent offset to the estimated access latency. This parameter change compensates for the non-linear seek time characteristics of limited stroke disk drives, enabling the RPO algorithm to make better command selection decisions that improve throughput while maintaining computational efficiency.
2Device complexity
If the maximum radial movement of the head is limited, then device complexity is reduced, but seek time performance worsens due to non-linear seek time relationships
Solution Approach 1:
The patent introduces an intermediary offset value that mediates between the physical limitation of the actuator stroke and the performance requirements of the RPO algorithm. This offset, which is a function of seek length, acts as a compensatory mechanism that translates the non-linear seek time characteristics into an adjusted access latency parameter, allowing the RPO algorithm to optimize command selection despite the limited stroke constraint.
3Manufacturing precision
If servo system parameters are adjusted for different seek distances, then positioning precision is improved, but the relationship between seek length and seek time becomes non-linear
Solution Approach 1:
The patent segments the seek operation into different distance ranges, with each segment having its own offset value added to the access latency. This segmentation approach allows the system to account for non-linear seek time relationships caused by different servo parameters while maintaining a relatively simple overall structure. The RPO algorithm can use these segmented offset values to make accurate throughput predictions without requiring complex non-linear models.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures that the performance of limited stroke disk drives matches that of full stroke disk drives across all command queue depths, maintaining consistent throughput by adjusting access latency according to seek length, thereby aligning average throughput curves.
Implementation Method 1
a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM)
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk, wherein a maximum radial movement of the head is limited. A plurality of access commands are stored in a command queue, and an access latency is determined for each command in the command queue, wherein the access latency is based at least on a seek latency for the head and a rotational latency for the disk. The access latency for each access command is increased by an offset based at least on a seek length for each access command, wherein the offset compensates for the limited maximum radial movement of the head. An access command is selected from the command queue based on the increased access latencies, and the selected access command is executed.