Magnetic Disk Write Control for SMR Track Error Prevention
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Solution Overview
Problem
Magnetic disk apparatuses face challenges in preventing data loss due to track errors caused by adjacent track interference during shingled magnetic recording (SMR) due to narrowed track widths, which traditional error correction methods struggle to address effectively.
Innovation Solution
The magnetic disk apparatus incorporates a controller that monitors the position of the magnetic head during writing, calculates a cumulative amount of track narrowing, and interrupts the write operation when the cumulative amount exceeds a threshold, allowing for a rotational delay and re-evaluation of track error estimation to prevent data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If track width is narrowed to increase storage capacity in SMR, then storage density is improved, but track error rate increases due to adjacent track interference
Solution Approach 1:
The system performs preliminary monitoring of magnetic head position during write operations and calculates cumulative track narrowing amounts before actual data loss occurs. By detecting positioning deviations early and interrupting write operations proactively, the system prevents adjacent track interference from causing irreversible data corruption, thus maintaining reliability while enabling narrow track widths for higher storage capacity
Solution Approach 2:
The system continuously monitors magnetic head position using servo information, calculates the cumulative amount of track narrowing caused by write operations, and uses this feedback to determine when to interrupt write operations. This closed-loop feedback mechanism allows the system to adapt to actual positioning conditions and prevent track errors that would otherwise occur with narrow track widths, resolving the contradiction between storage density and reliability
2Reliability
If write operation is interrupted frequently to prevent track errors, then data integrity is improved, but write operation performance deteriorates
Solution Approach 1:
The system applies partial action by interrupting write operations only when the cumulative track narrowing amount exceeds a predetermined threshold, rather than interrupting continuously. This selective interruption approach prevents track errors and ensures data integrity while minimizing the impact on write operation performance, as write operations continue uninterrupted during normal conditions
Solution Approach 2:
The system dynamically adjusts the write operation state based on the calculated cumulative track narrowing amount. By changing the operational parameter (write operation status) from continuous to interrupted only when necessary, the system maintains high write performance during normal operation while ensuring data integrity when track narrowing becomes excessive
3Reliability
If cumulative track narrowing amount is monitored continuously, then track error prevention is improved, but computational load increases
Solution Approach 1:
The system performs preliminary calculations of the cumulative track narrowing amount using servo information that is already available during normal operation. By utilizing pre-existing servo data and performing calculations in advance before track errors occur, the system achieves reliable track error prevention without requiring excessive additional computational resources
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 frequency of partial track slip operations, maintains write operation performance, and ensures data integrity by minimizing unnecessary interruptions and data sector depletion.
Implementation Method 1
A magnetic head 22 writes and reads data to and from the magnetic disk 11
Implementation Method 2
The controller is configured to read servo information when the magnetic head passes over each of the multiple servo sectors and execute, based on the read servo information, a write operation on the first track while executing positioning of the magnetic head on the first track
Data Source
AI summary
According to an embodiment, a controller executes a determination operation when a magnetic head passes over a servo sector during a write operation. In the determination operation, a first cumulative amount is calculated by accumulating, for a first section, evaluation amounts each corresponding to an amount by which the width of an adjacent track is narrowed due to the write operation, and determination is made as to whether the first cumulative amount is smaller or larger than a threshold value corresponding to a limit of error correction. When the first cumulative amount is determined to be larger than the threshold value, the controller interrupts the write operation and re-executes the determination operation after executing a rotational delay. The controller resumes the write operation when the first cumulative amount is determined to be smaller than the threshold value as a result of the re-executed determination operation.