ZNS SSD Zone-Based Garbage Collection to Reduce Write Amplification
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Solution Overview
Problem
Zoned Namespace (ZNS) SSDs face challenges in managing data overwrites within zones, leading to increased write amplification factor (WAF) due to the need for overprovisioned superblocks to accommodate both sequential and random writes, which complicates the mapping process and increases resource utilization.
Innovation Solution
Implementing a zone-based garbage collection process that relocates valid data from overprovisioned superblocks to a single superblock for each zone, while refraining from relocating data from superblocks associated with different zones, thereby optimizing memory usage and reducing WAF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If overprovisioned superblocks are used to accommodate both sequential and random writes in ZNS SSDs, then the storage device can handle different write patterns, but the write amplification factor increases and resource utilization becomes inefficient
Solution Approach 1:
The patent segments the storage space into zone-specific superblocks, where each superblock is dedicated to storing data from a specific zone. This segmentation allows the garbage collection process to selectively relocate only the necessary data blocks associated with the target zone, rather than relocating all valid data in the superblock. Consequently, this reduces the write amplification factor by minimizing unnecessary data relocation while maintaining the adaptability to handle both sequential and random writes.
2Adaptability or versatility
If overprovisioned superblocks are used to accommodate both sequential and random writes, then different write patterns can be supported, but memory usage becomes inefficient
Solution Approach 1:
By segmenting superblocks into zone-specific units, the patent enables precise tracking and management of data blocks belonging to different zones. During garbage collection, only data blocks associated with the target zone are relocated to the appropriate zone-specific superblock, leaving other data blocks untouched. This approach optimizes memory usage by eliminating redundant data relocation and improving the efficiency of memory utilization while preserving the capability to support diverse write patterns.
3Reliability
If traditional garbage collection relocates all valid data in a superblock, then data integrity is maintained, but the mapping process becomes complicated and resource utilization increases
Solution Approach 1:
The patent introduces zone-specific superblocks that are dedicated to storing data from specific zones. This segmentation simplifies the mapping process by establishing a direct correspondence between zones and their respective superblocks. During garbage collection, the system only needs to track and relocate data blocks within the same zone, significantly reducing the complexity of the mapping process compared to traditional approaches that require tracking all valid data across entire superblocks while maintaining data integrity.
4Reliability
If traditional garbage collection relocates all valid data, then data integrity is ensured, but resource utilization becomes inefficient
Solution Approach 1:
By organizing storage into zone-specific superblocks, the patent enables the garbage collection process to selectively relocate only the data blocks associated with the target zone. This selective approach ensures data integrity for the zones being collected while avoiding unnecessary relocation of data blocks from other zones. As a result, resource utilization is improved by reducing the total amount of data that needs to be read, processed, and rewritten during garbage collection operations.
Data Source
AI summary
Aspects of a storage device are provided including zone-based GC in a ZNS. The storage device includes a NVM and a controller. The NVM includes first blocks, second blocks, and third blocks. The controller creates a first superblock including the first blocks, a second superblock including the second blocks, and a third superblock including the third blocks. The controller allocates a first sub-drive including the first superblock for storing data overwrites and a second sub-drive including the second and third superblocks for storing sequential data in the NVM. During GC for superblocks respectively including data for a specific zone, the controller relocates written data for this zone from the first and third superblocks to the second superblock while refraining from relocating data associated with other zones from the first superblock to the second superblock. As a result, storage device cost, overprovisioning, and WAF may be reduced.