Magnetic Disk Sector Reallocation for Defect Prevention
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Solution Overview
Problem
Magnetic disk devices face performance deterioration due to age-related defects in sectors near registered defective sectors, as minor defects detected before shipment may not be registered, leading to read errors and reduced performance over time.
Innovation Solution
A magnetic disk device with a controller that identifies and reallocates addresses for sectors likely to become defective, registering them in lists (P and G lists) and replacing them with alternative sectors to prevent read performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If defective sectors are registered in P list based on inspection before shipment, then sectors with minor defects (thin scratches) may be included, but this causes read performance deterioration over time due to age-related deterioration and growth of scratches in nearby sectors
Solution Approach 1:
The system performs preliminary actions by detecting and registering sectors that are likely to become defective in the future (before they actually fail) into the P list. When a defective sector is detected, the system proactively registers adjacent sectors that show signs of potential future failure, rather than waiting for them to actually fail. This preliminary registration prevents read performance deterioration by replacing these sectors before they become truly defective.
2Reliability
If sectors with minor defects are registered in P list, then comprehensive defect coverage is achieved, but this leads to increased number of defective sectors in P list and G list causing performance degradation
Solution Approach 1:
The system applies local quality by making differentiated decisions about sector registration based on their specific characteristics and locations. Not all sectors are treated uniformly - only sectors that meet specific criteria (adjacent to defective sectors, showing potential failure signs) are registered in the P list. This selective approach ensures comprehensive coverage of truly at-risk sectors while avoiding unnecessary registration of healthy sectors, thus maintaining read performance.
3Reliability
If reallocation of addresses for defective sectors is performed, then data access reliability is maintained, but this requires additional controller operations and processing overhead
Solution Approach 1:
The reallocation process is performed as a preliminary action when defective sectors are first detected and registered in the P list, rather than waiting for actual read failures to occur. By proactively reallocating addresses during the registration phase, the system maintains data access reliability while minimizing the complexity of operations during normal read/write operations, as the mapping is already established in advance.
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a disk that includes a plurality of tracks, each track including a plurality of sectors for storing data, a head that is for writing data to the plurality of sectors and reading data from the plurality of sectors, and a controller. The controller is configured to determine that a first sector of the plurality of sectors is not able to be read and is a defective sector, determine that a second sector of the plurality of sectors is disposed along a line that extends through the first sector and a defective sector included in a first list of defective sectors, register the second sector in the first list of defective sectors, and reallocate an address corresponding to the second sector to a first alternative sector included on the disk.