Hard Disk Drive High Track Misregistration Data Preservation
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Solution Overview
Problem
High track misregistration (TMR) in magnetic recording hard disk drives (HDDs) leads to data overwriting and unrecoverable data issues due to adjacent track encroachment, with existing solutions either decreasing data density or causing continuous write inhibit, degrading performance.
Innovation Solution
The HDD operates in multiple modes, enabling high TMR mode when position error signal exceeds a threshold, using a buffer to store and correct data from adjacent tracks, and switching to hibernation mode when buffer fill exceeds a threshold, allowing continued data integrity and density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data tracks are placed closer together to increase data density, then data track density is improved, but adjacent track encroachment occurs causing data loss
Solution Approach 1:
The system performs preliminary reading and buffering of adjacent track data before writing operations. When track misregistration is detected, the previously buffered data from adjacent tracks can be recovered and rewritten, preventing permanent data loss despite higher track density
Solution Approach 2:
A buffer memory is introduced as an intermediary between the read/write head and the data tracks. This buffer temporarily stores data from adjacent tracks, allowing the system to recover from write field encroachment by rewriting data from the buffer when misregistration occurs
2Reliability
If write inhibit is continuously enabled to prevent adjacent track encroachment, then data integrity is improved, but write performance deteriorates
Solution Approach 1:
The write inhibit mechanism is made dynamic rather than static. The system continuously monitors position error signals and only inhibits writing when actual misregistration exceeds thresholds, allowing normal writing operations to proceed when positioning is accurate, thus maintaining high write performance while preventing data loss
3Reliability
If buffer size is increased to store more adjacent track data for correction, then data recovery capability is improved, but memory usage increases
Solution Approach 1:
The buffer memory is allocated selectively rather than universally. Instead of buffering all tracks, the system buffers only adjacent track data that is likely to be affected by write field encroachment during high-density operations, optimizing memory usage while maintaining data recovery capability
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
Enables increased data track density and operational reliability in high TMR environments by correcting adjacent track erasure and managing buffer fill, maintaining performance and data integrity.
Implementation Method 1
magnetic recording hard disk drives (HDDs)
Implementation Method 2
data on the adjacent tracks is read
Implementation Method 3
the position error signal (PES) from the servo positioning information in the data tracks
Data Source
AI summary
A hard disk drive (HDD) has a high track misregistration (TMR) mode of writing data. If the position error signal (PES) from the servo positioning information exceeds a first write inhibit threshold (WI-1), writing is not inhibited but a high TMR mode of operation is enabled. In high TMR mode, prior to writing data to the target track, the data on the adjacent tracks is read and stored in a buffer. The data to be written to the target track is also stored in the buffer, and is flagged to indicate that the data needs to be written. The data is then written to the target track. However, if during writing the PES exceeds a second threshold (WI-2), then the data from the adjacent encroached track in the buffer is flagged for writing and the process repeated with the encroached track set as the target track.