Rotational Positioning Optimization for Off-Track Write Mitigation

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Solution Overview

Problem

Existing data storage devices face challenges in minimizing the risk of off-track write (OTW) events during seek operations, which can lead to data integrity issues and performance degradation.

Innovation Solution

The implementation of a rotational positioning optimization (RPO) system that selects a seek time model based on the operational characteristics of access commands, specifically using a slow seek time model for off-track-susceptible seek access patterns to introduce a penalty and reduce the risk of OTW events.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a fast seek time model is used to minimize access time, then I/O performance is improved, but the risk of off-track write events increases

Engineering Contradiction:

ImproveI/O performanceVSAvoidrisk of off-track write events

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system dynamically selects between different seek time models (fast and slow) based on the specific access command characteristics and current drive state. The controller evaluates factors such as seek length, current position, and recent access patterns to determine which model to apply, allowing the seek time to be adaptive rather than fixed. This resolves the contradiction by using fast seek times when safe and slow seek times when off-track risk is detected.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the parameter of seek time estimation by switching between different mathematical models. The fast seek time model provides aggressive timing for performance-critical operations, while the slow seek time model provides conservative timing that includes penalty factors for off-track susceptibility. This parameter change allows the system to optimize for either performance or reliability depending on the operational context.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If additional seek time is added to attenuate vibration in PES, then off-track write risk is reduced, but access time increases

Engineering Contradiction:

Improveoff-track write risk reductionVSAvoidaccess time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system applies different seek time characteristics to different access commands based on their specific properties. Not all seeks receive the same treatment - only those identified as off-track-susceptible (such as short seeks following long seeks, or seeks across certain radial distances) receive the slow seek time model with vibration attenuation. Other seeks use the fast model, minimizing unnecessary time delays. This local differentiation resolves the contradiction by applying caution only where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The controller performs preliminary evaluation of access commands before execution, analyzing factors such as seek length, current head position, recent access patterns, and drive state to predict off-track risk in advance. Commands identified as susceptible to off-track writes are pre-flagged and assigned the slow seek time model, which includes preliminary vibration attenuation delays. This preliminary action allows the system to prevent off-track writes before they occur while minimizing overall time loss by only applying delays to at-risk commands.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If multiple seek time models are implemented, then off-track susceptibility can be managed, but device complexity increases

Engineering Contradiction:

Improveoff-track susceptibility managementVSAvoidcontrol circuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The control circuitry is designed to handle multiple seek time models through a unified command scheduling framework. The same basic scheduler that manages normal I/O operations also manages the selection between fast and slow seek time models, and the same control algorithms that handle normal seeks handle vibration-attenuated seeks. This multi-functional approach allows the system to manage off-track susceptibility without requiring entirely separate control paths, thereby limiting the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250117159A1Data storage device sorting access commands based on performance and off-track mitigation optimization

Publication Date: 2025.04.10 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

Various illustrative aspects are directed to a data storage device, method, and one or more processing devices that are configured to: select a seek time model from a plurality of seek time models based at least in part on an operational characteristic of an access command, the operational characteristic relating to an off-track susceptibility of executing the access command; determine an access time for the access command using the selected seek time model; and select a next access command for execution based on the determined access time for the access command and determined access times for other ones of a plurality of access commands.