Write Encroachment Mitigation via Threshold Flagging and Cache
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Solution Overview
Problem
Data storage devices face challenges in preventing write encroachment between adjacent tracks in recording media, where existing methods halt writing when the write fault threshold is exceeded, leading to performance impacts and potential data loss due to single-sided or dual-sided encroachment.
Innovation Solution
A write encroachment threshold (WET) system is introduced, which flags tracks as off-track and unwriteable when the position error signal exceeds the WET but not the write fault threshold, redirecting writes to a media cache to avoid encroachment, and enables data recovery during idle time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the write fault threshold is used to prevent write encroachment, then data integrity is improved, but writing performance deteriorates due to frequent halting
Solution Approach 1:
The system performs preliminary actions by detecting off-track conditions using the position error signal before actual write encroachment occurs. When the PES exceeds the WET threshold, the system proactively flags the track and redirects writes to cache, preventing encroachment before it compromises data integrity while maintaining smoother write operations compared to reactive threshold halting
Solution Approach 2:
The media cache serves as an intermediary buffer between the write operations and the flagged tracks. When tracks are flagged as unwriteable due to off-track conditions, the cache temporarily holds the write data, allowing the write operation to continue without halting while preventing encroachment on adjacent tracks
2Reliability
If a lower WET threshold is used to detect off-track conditions, then encroachment prevention is improved, but track flagging frequency increases
Solution Approach 1:
The system introduces a new parameter threshold (WET) that is lower than the traditional write fault threshold. This parameter change allows detection of off-track conditions at earlier stages, enabling preventive action before actual encroachment occurs. The dual-threshold approach (WET for detection, higher threshold for critical failure) optimizes both prevention effectiveness and track availability
Solution Approach 2:
When tracks are flagged as unwriteable due to exceeding the WET threshold, the system temporarily discards writes to those tracks by redirecting them to the media cache. During idle time, the system recovers by transferring the cached data back to the original tracks, minimizing permanent loss of track availability while ensuring encroachment prevention
Data Source
AI summary
The disclosed technology provides for a method and system comprising determining a write-encroachment threshold of a recording medium, determining a track as off-track and one or more tracks substantially near the off-track as unwriteable, flagging the one or more tracks substantially near the off-track track, and writing write data for the one or more flagged tracks to a media cache. In a recovery process, the write data can be later transferred back to the flagged tracks.