Disk Drive Off-Track Error Recovery in Multi-Actuator Drives
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Solution Overview
Problem
Magnetic hard disk drives (HDDs) with multiple rotary actuators face positioning accuracy issues due to mechanical interactions, leading to off-track errors that cause significant delays in data access operations.
Innovation Solution
Implementing a method where the disk access operation is retried for sectors associated with off-track errors without requiring additional revolutions for each data track, allowing completion of sequential disk access operations in fewer revolutions, and in some cases, as few as one or two additional revolutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple rotary actuators are used to increase throughput, then data access speed is improved, but positioning accuracy deteriorates due to mechanical interactions between actuators
Solution Approach 1:
The patent segments the data access operation into multiple attempts across different disk revolutions. When an off-track error is detected during sequential write operations, the system divides the affected sectors into groups and attempts to write them in subsequent revolutions, rather than requiring all sectors to be written in a single revolution. This segmentation allows the system to maintain high throughput with multiple actuators while recovering from positioning errors over multiple attempts.
Solution Approach 2:
The patent implements preliminary error detection and recovery planning during the disk access operation. Before completing the write operation, the system monitors for off-track errors and prepares recovery strategies by identifying affected sectors and planning subsequent write attempts. This preliminary action enables efficient recovery without significantly impacting overall throughput.
2Reliability
If conventional off-track error recovery is used with additional revolution for each affected track, then data integrity is improved, but access time increases significantly
Solution Approach 1:
The patent merges multiple recovery operations into a single additional disk revolution. Instead of performing separate recovery operations for each affected data track, the system identifies all sectors experiencing off-track errors across multiple tracks and consolidates them into groups that can be recovered simultaneously in one or two additional revolutions. This merging approach maintains data integrity while significantly reducing the time penalty compared to conventional track-by-track recovery.
Solution Approach 2:
The patent applies partial recovery action by focusing only on the specific sectors affected by off-track errors rather than re-attempting to write all sectors on affected tracks. The system identifies and recovers only the necessary portions of data, avoiding unnecessary write operations and reducing overall recovery time while ensuring data completeness.
Data Source
AI summary
In a disk drive, when an off-track error occurs during a sequential disk access operation that spans multiple contiguous data tracks, efficient recovery is performed. In an embodiment, the disk access operation (e.g., reading from or writing to a disk) is attempted for all sectors of the sequential disk access operation. The disk access operation is then attempted again for sectors associated with any off-track errors that occurred during the disk access operation. In another embodiment, when an off-track error occurs during a sequential write operation in a shingled magnetic recording drive, the data originally targeted to be written to a first portion is written to a second portion of the data track that follows the first portion. Since no additional revolutions of the disk are needed for data associated with the sequential write operation to be written to the disk.