Disk Drive Write Unsafe Threshold Adjustment for Unrecoverable Servo Sectors
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Solution Overview
Problem
Existing disk drive systems face challenges in maintaining accurate head positioning during write operations due to unrecoverable servo compensation values, which can lead to increased latency and data relocation issues when the compensation value is defective, causing the write operation to be aborted unnecessarily.
Innovation Solution
The write unsafe threshold is dynamically adjusted by reducing it from a first threshold to a second, lower threshold when a servo sector's compensation value is unrecoverable, allowing the write operation to continue if the adjusted position error signal does not exceed this new threshold, thereby minimizing latency and data relocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the write unsafe threshold is set to a higher value to allow more write operations to proceed, then productivity is improved, but reliability deteriorates due to increased risk of data corruption from unrecoverable servo sectors
Solution Approach 1:
The patent applies dynamics by making the write unsafe threshold adjustable rather than fixed. The threshold dynamically changes based on servo sector conditions: a first threshold is used when servo compensation values are recoverable, and a second (lower) threshold is used when unrecoverable servo sectors are detected. This dynamic adjustment allows the system to optimize between productivity and reliability based on real-time disk conditions.
Solution Approach 2:
The patent implements parameter changes by modifying the write unsafe threshold parameter according to the state of servo compensation values. When unrecoverable servo sectors are detected, the threshold parameter is changed from the first value to the second value, enabling the system to adapt its write safety criteria based on the actual condition of the disk surface.
2Reliability
If the write unsafe threshold is reduced to maintain data integrity when servo compensation values are unrecoverable, then reliability is improved, but productivity deteriorates due to increased abort rate of write operations
Solution Approach 1:
The patent applies local quality by differentiating the write safety criteria based on the local condition of servo sectors. Instead of applying a uniform threshold across the entire disk, the system applies a stricter second threshold specifically when unrecoverable servo sectors are detected, while maintaining the more permissive first threshold when servo sectors are healthy. This localized approach to quality control optimizes both reliability and productivity.
3Reliability
If write operations are aborted when servo compensation values are unrecoverable, then reliability is improved by preventing data corruption, but loss of time increases due to retry operations and data relocation
Solution Approach 1:
The patent applies partial action by using a second threshold that is lower than the first threshold but not necessarily zero or extremely restrictive. This partial restriction allows some write operations to proceed even when unrecoverable servo sectors are present, as long as the position error signal remains below the second threshold. This approach prevents complete abortion of write operations while still maintaining enhanced safety, thereby reducing time loss compared to absolute abortion strategies.
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 the likelihood of aborting write operations due to defective servo sectors, maintaining data integrity and reducing latency by allowing the disk drive to glide through unrecoverable servo sectors without retrying the entire write operation, thus enhancing the overall performance and reliability of the disk drive.
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)
Implementation Method 2
A position error signal (PES) is generated by reading the servo bursts 14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track
Data Source
AI summary
A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors, wherein each servo sector comprises servo data and a servo compensation value. While servoing a head over a target data track during a write operation, a position error signal (PES) is generated at each servo sector based at least in part on the servo data. When the servo compensation value of a first servo sector is recoverable, the write operation is aborted when the PES generated at the first servo sector exceeds a first write unsafe threshold. When the servo compensation value of the first servo sector is unrecoverable, the write operation is aborted when the PES generated at the first servo sector exceeds a second write unsafe threshold less than the first write unsafe threshold.