Disk Drive Head Sorting by Radial Location
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Solution Overview
Problem
In disk drives, access commands are delayed or 'locked out' when heads are near the outer or inner diameter of the disk surfaces due to increased seek length, leading to higher average and tail latency, as existing sorting algorithms do not adequately account for the radial location of heads during seek operations.
Innovation Solution
The control circuitry sorts access commands based on scalars that adjust seek time and probability of selection based on the current and target radial locations of the heads, using a split actuator design with multiple VCMs to optimize execution order and reduce latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If existing sorting algorithms are used for access commands, then the sorting process is simple, but heads near outer or inner diameter experience increased seek length and higher latency
Solution Approach 1:
The patent applies local quality by implementing location-aware sorting that treats different radial positions on the disk differently. The sorting algorithm assigns different weights and priorities to access commands based on whether they target inner diameter, outer diameter, or middle regions. This localized treatment optimizes seek performance for heads at different positions without requiring complete redesign of the sorting mechanism.
Solution Approach 2:
The patent changes the sorting parameters by introducing location-based weighting factors and modifying the sort key calculation to include radial position information. Instead of using simple cylinder-order sorting, the system dynamically adjusts sorting parameters based on head location, transforming the sorting behavior to account for varying seek characteristics across different disk regions.
2Productivity
If access commands are sorted without considering head radial location, then the sorting process is fast, but heads near outer or inner diameter are delayed or locked out
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing sort keys that incorporate radial location information for all pending access commands. Before executing the sort operation, the system enriches each command with location-aware metadata, allowing the sorting algorithm to efficiently prioritize commands for heads at outer or inner diameters without adding computational overhead during the actual sorting execution.
3Loss of time
If scalar weighting based on radial location is applied, then latency for outer/inner diameter is reduced, but the sorting computation becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the disk surface into distinct radial zones (inner diameter region, middle region, outer diameter region) and applying different sorting weights and priorities to commands targeting each zone. This segmentation allows the system to use simple weight multiplication for each zone rather than complex continuous calculations, reducing computational complexity while maintaining location-aware optimization.
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 reduces latency and improves access times by prioritizing access commands when heads are near the outer or inner diameters, ensuring efficient head positioning and minimizing delays.
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) to position the head radially over the disk
Data Source
AI summary
A data storage device is disclosed comprising a first plurality of heads actuated over a first subset of disk surfaces by a first actuator, and a second plurality of heads actuated over a second subset of disk surfaces by a second actuator. A plurality of access commands is received, wherein each access command is associated with one of the heads. A scalar is configured for each access command based on at least one of a current radial location of the corresponding head or a target radial location of the corresponding head associated with executing the access command. The access commands are sorted based on the scalars, and one of the access commands is selected for execution based on the sort.