Magnetic Disk Eccentricity Measurement for Shingled Write Offset
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Solution Overview
Problem
In magnetic disk devices using shingled magnetic recording, changes in disk eccentricity can lead to dynamic offset, causing data written to adjacent tracks to be erased, as the corrected eccentricity values differ before and after such changes, affecting write process accuracy.
Innovation Solution
The magnetic disk device measures the current eccentricity and compares it to the previous value, calculating a new corrected value when a change is detected, and restarts the write process from a shifted position to maintain data integrity by using the updated eccentricity value for write dynamic offset control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the magnetic disk device uses shingled magnetic recording to increase storage capacity, then the track density is improved, but the data integrity of adjacent tracks becomes vulnerable to erasure when disk eccentricity changes
Solution Approach 1:
The system performs preliminary actions by measuring disk eccentricity before writing data to adjacent tracks and storing the measured value. When writing resumes after interruption, the system compares the current eccentricity measurement with the stored preliminary value and adjusts the write position accordingly, preventing data erasure while maintaining high track density
Solution Approach 2:
The system implements feedback by continuously monitoring disk eccentricity and using the measured values to adjust write operations. The controller compares current eccentricity measurements with previously stored values and modifies the write position based on the difference, ensuring data integrity is maintained despite changes in disk eccentricity
2Manufacturing precision
If the magnetic disk device performs write dynamic offset control to adjust the R/W offset value, then the dynamic offset is controlled, but the write process complexity increases when eccentricity changes occur
Solution Approach 1:
The system measures and stores the disk eccentricity value before the write process begins. This preliminary measurement allows the controller to pre-calculate the appropriate write position adjustments, simplifying the write process during execution while maintaining precision
Solution Approach 2:
The system changes the write position parameter based on the measured eccentricity values. By adjusting the write position according to the difference between current and stored eccentricity measurements, the system maintains write accuracy without requiring complex real-time calculations during the write process
3Ease of operation
If the magnetic disk device restarts the write process from the same position after interruption, then the write operation is simple, but data erasure occurs when eccentricity has changed
Solution Approach 1:
The system performs preliminary eccentricity measurement and storage before writing. When resuming the write process after interruption, the controller uses the stored preliminary value and compares it with the current measurement to determine the appropriate restart position, preventing data erasure while maintaining operational simplicity
Solution Approach 2:
The system uses feedback from eccentricity measurements to adjust the restart position. By comparing current and stored eccentricity values and using this information to modify the restart position, the system ensures data integrity is maintained without significantly complicating the write process
Data Source
AI summary
According to one embodiment, a magnetic disk device including a disk, and a controller which calculates a first corrected value based on a first eccentricity of the disk, and writes a first track based on the first corrected value, wherein when the controller interrupts the process for writing the second track so as to overlap the first track at a first position, the controller measures a second eccentricity of the disk, and compares the first eccentricity with the second eccentricity, and when the first eccentricity is different from the second eccentricity, the controller restarts the process for writing the second track from a second position away from the first position in a radial direction.