Unshingled Cache Regions in Shingled Magnetic Recording Drives
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Solution Overview
Problem
Shingled magnetic recording (SMR) devices face challenges in data integrity during write caching due to the limitations of conventional RAM caches, which can lead to data loss during power failures and inefficiencies in sequential writing, especially since physical block addresses change dynamically with each write operation.
Innovation Solution
The introduction of unshingled cache regions organized in concentric bands on the disk media, which can be used for efficient data storage and as a 'hot cache' for frequently written data, allowing for nonsequential writing and reducing seek times, and are adaptable to be dynamically created or removed to optimize performance and avoid data overwrites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional RAM caches are used for write caching in SMR devices, then write performance can be improved, but data integrity is compromised due to potential data loss during power failures
Solution Approach 1:
The cache memory is segmented into multiple independent cache regions, each capable of storing write cache data separately. This segmentation allows the system to isolate data loss to individual regions while preserving data in other regions, thereby improving overall data integrity while maintaining write performance benefits
Solution Approach 2:
The system creates redundant copies of write cache data in multiple cache regions before potential data loss can occur. This beforehand cushioning ensures that even if one cache region loses data due to power failure, the redundant copies remain intact, protecting data integrity while enabling aggressive write caching
2Reliability
If shingled tracks are written sequentially from ID to OD, then data integrity is maintained, but seek times increase for nonsequential writing operations
Solution Approach 1:
The storage medium is divided into multiple independent cache regions that can be accessed independently. This allows the system to perform nonsequential write operations to different cache regions without requiring sequential track access, reducing seek times while maintaining data integrity through proper cache management
Solution Approach 2:
The multiple cache regions serve as intermediary storage between the host system and the sequential shingled I-regions. Data can be written to cache regions in nonsequential order for improved performance, then transferred to I-regions in sequential order, mediating between performance requirements and data integrity constraints
3Adaptability or versatility
If physical block addresses are dynamically changed with each write operation, then storage flexibility is improved, but system complexity increases due to address mapping overhead
Solution Approach 1:
The address mapping system is segmented into region-specific mapping tables for each cache region. This reduces the complexity of managing dynamic PBA changes by localizing address translation to individual regions rather than requiring a single complex global mapping system, while still providing the flexibility of dynamic address assignment
Data Source
AI summary
Shingled magnetic recording (SMR) devices according to embodiments of the invention include unshingled cache regions that can be used for storage of data. The unshingled cache regions can be used in a variety of flexible ways including in an implementation of write-twice caching or for opportunistic temporary storage to improve performance. The cache regions can be offset between top and bottom surfaces of the disk and staggered between disks to provide shorter seek times to the nearest cache region. Embodiments of the invention are adapted for use with symmetric or asymmetric heads.