Disk Storage Drift-Off Write Data Protection
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Solution Overview
Problem
The shingled write method in disk storage apparatuses can result in 'drift-off write' phenomena, where the head deviates from the track centerline, leading to data degradation and potential loss, especially when data is written partially overlapping adjacent tracks, causing adjacent data to be overwritten and becoming unreadable.
Innovation Solution
A disk storage apparatus with a controller that detects drift-off writes, determines the affected area, and implements a data protection process by using a nonvolatile cache area to securely store adjacent data, allowing for re-writing along the track centerline and preventing data degradation, while maintaining the integrity of adjacent data by storing it in a buffer or backup area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If shingled write method is used to achieve high storage capacity, then storage capacity is improved, but data reliability deteriorates due to drift-off write causing data degradation
Solution Approach 1:
The system performs preliminary detection of drift-off writes during the shingled write process. When drift-off is detected, the system proactively protects the affected adjacent track data by storing it in a buffer or backup area before the data can be degraded, thereby preventing data reliability issues while maintaining high storage capacity
Solution Approach 2:
A buffer area or backup area is introduced as an intermediary storage space between the write head and the final data storage location. This intermediary area temporarily holds adjacent track data during shingled write operations, allowing the system to protect data from drift-off degradation while maintaining the high storage capacity benefits of shingled write
2Reliability
If head is repositioned to prevent drift-off write, then data reliability is improved, but writing speed deteriorates
Solution Approach 1:
The system extracts and separates the data protection function from the main write operation. By detecting drift-off writes and protecting adjacent track data through a separate buffer/backup mechanism, the system maintains writing speed while improving data reliability, avoiding the need to slow down the main write process
Solution Approach 2:
The system implements feedback control by continuously monitoring the write head position during shingled write operations. When drift-off is detected through position feedback, the system activates protection mechanisms for adjacent tracks while maintaining the overall write speed, balancing reliability and performance
3Reliability
If adjacent track data is protected by storing in buffer area, then data integrity is improved, but device complexity increases
Solution Approach 1:
The buffer area or backup area serves multiple functions: it protects adjacent track data from drift-off degradation, maintains data integrity during shingled write operations, and enables rapid data recovery if needed. This multi-functionality justifies the added complexity by providing comprehensive data protection without requiring separate dedicated systems
Solution Approach 2:
The system creates a copy of adjacent track data in the buffer or backup area when drift-off is detected. This copying mechanism provides data integrity protection with relatively simple implementation, as it only requires duplicating data temporarily rather than implementing complex error correction or recovery systems
Data Source
AI summary
A disk storage apparatus according to one embodiment includes a head, a storage device, a write module and a controller. The head writes data on a disk. The storage device has a storage area for temporarily storing the data written by the head. The write module writes data to tracks on a disk, while partially overlapping the data with previously written data to adjacent track. The controller detects a drift-off write of the head while writing data, determines a drift-off write area in which the drift-off write is occurred, and protects the data written in the storage area, if the data is written in the drift-off write area.