On-Demand Parity Sectors for SMR Squeeze-Error Correction
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Solution Overview
Problem
Shingled Magnetic Recording (SMR) drives face challenges in error correction, particularly 'squeeze-errors' where writing a second track introduces errors in adjacent tracks, and existing error correction codes are not scalable or efficient for SMR architectures, especially in archival applications requiring high data integrity and increased tracks per inch.
Innovation Solution
A two-level error correction system is implemented, using fixed parity sectors for initial correction and generating additional on-demand parity sectors when needed, which are stored separately, allowing for dynamic error correction beyond the initial capability, thereby avoiding track rewriting and enhancing data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If shingled magnetic recording is used to increase areal density, then storage capacity increases, but squeeze-errors occur when writing adjacent tracks
Solution Approach 1:
The system performs preliminary error detection after writing each track in the shingled sequence. By detecting squeeze-errors immediately after the interfering track is written, the system can proactively generate corrective parity information before data corruption becomes permanent, thus maintaining reliability while enabling high-density shingled recording
Solution Approach 2:
The invention introduces an intermediary error correction mechanism that acts between the write head and the stored data. This intermediary system generates parity sectors that serve as a buffer, allowing the system to correct squeeze-errors that occur during shingled writing without compromising the integrity of the stored data
2Reliability
If fixed parity sectors are used for error correction, then error correction capability is provided, but additional parity overhead reduces storage efficiency
Solution Approach 1:
The system dynamically adjusts the amount of parity information generated based on the actual error conditions detected. Rather than applying fixed parity overhead to all tracks, the system generates additional parity sectors only when squeeze-errors are detected, making the error correction mechanism adaptive to actual storage conditions and minimizing unnecessary overhead
Solution Approach 2:
The invention changes the parameter of parity sector quantity from a fixed value to a variable value based on detected error conditions. When no squeeze-errors are present, minimal or no additional parity is applied. When errors are detected, the system increases parity sector generation accordingly, optimizing the balance between reliability and storage efficiency
3Reliability
If on-demand parity sectors are generated for tracks with errors, then data retrieval reliability improves, but system complexity increases
Solution Approach 1:
The system implements self-service error correction by automatically detecting squeeze-errors and generating the necessary parity information without external intervention. The error correction process is embedded within the normal write operations, allowing the system to service its own errors through automated parity generation and correction, thereby improving reliability without requiring complex external error correction infrastructure
Data Source
AI summary
Data storage devices are described with an ECC system that generate additional on-demand ECC information for a previously written track to provide for correction of data errors in the track and thereby avoid having to rewrite the track. Embodiments of the invention address the squeeze-error problem that arises when writing the next (second) track in a sequence causes errors to be introduced in the adjacent previously written (first) track. In alternative embodiments the existence of the data errors in the first track can be detected by reading the track or by estimating the number of likely errors using head position data measured while writing the first and second tracks. The additional on-demand ECC information can be written on any track that is available.