Dual-Layer FTL Consolidation Using uRegion Update Selection
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Solution Overview
Problem
Existing storage devices face challenges in efficiently consolidating updates in the update layer (uLayer) of dual-layer Flash Transition Layer (FTL) due to limited RAM, leading to rapid overflow and reduced Random Write (RW) performance.
Innovation Solution
The controller generates copies of uRegion headers before a control sync operation, selects the best uRegion for consolidation based on uRun differences, reads selected mSets from flash to cache, and merges updated uRuns, optimizing consolidation by reducing unnecessary updates and write amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the uLayer is maintained with a small constant size in limited RAM, then device capacity is preserved, but the uLayer overflows quickly requiring frequent consolidation
Solution Approach 1:
The system performs control sync operations to proactively consolidate uLayer updates before the uLayer becomes completely full. By periodically syncing uLayer data to the mLayer and flash memory, the system prevents overflow conditions and maintains write performance without requiring a larger uLayer buffer.
Solution Approach 2:
The consolidation process operates periodically based on uLayer fill conditions. The controller monitors uLayer usage and triggers consolidation operations at appropriate intervals, balancing the need to maintain uLayer capacity for recent updates against the need to prevent overflow and maintain performance.
2Productivity
If consolidation is performed frequently to prevent uLayer overflow, then Random Write performance is maintained, but write amplification increases
Solution Approach 1:
The controller monitors uLayer usage metrics and consolidation history to intelligently determine when consolidation is necessary. By using feedback from uLayer fill levels and update patterns, the system performs consolidation only when needed, avoiding excessive write operations while maintaining performance.
Solution Approach 2:
The system dynamically adjusts consolidation timing and thresholds based on workload patterns and uLayer utilization. By changing the parameters of when and how consolidation occurs based on real-time conditions, the system optimizes the balance between maintaining performance and minimizing write amplification.
3Ease of manufacture
If the uLayer is divided into segments like the mLayer, then consolidation becomes simpler, but the irregular structure of uLayer makes segmentation non-trivial
Solution Approach 1:
The uLayer is logically divided into uRegion segments that can be independently managed and consolidated. Each uRegion contains a subset of the update mappings, allowing the controller to perform consolidation on individual regions rather than the entire uLayer at once, simplifying the consolidation process while respecting the underlying irregular structure.
4Quantity of substance
If a large mLayer is used to store all mappings, then mapping capacity is sufficient, but the size of mLayer increases requiring more flash memory
Solution Approach 1:
The system extracts frequently updated mapping entries from the mLayer and stores them in the uLayer buffer in RAM. This allows the majority of the mapping table to remain in flash memory in a compact form, while only the active updates are maintained in the smaller uLayer structure, reducing the effective size requirement of the overall mapping system.
Data Source
AI summary
The present disclosure generally relates to improved consolidation in dual-layer FTL. In preparation for the next control sync, the controller will generate a copy the uRegions uHeaders and will continue updating the uLayer uRegion with new uRun entries. After completing the control sync operation, the controller will then select the best consolidation candidate based on comparing the uRegion uHeaders with their copy and determining the uRegion with the maximum uRuns difference or the greatest number of uRun updates in case the uRun updates difference is less than a threshold. The controller then reads the selected mSets from the flash memory to its cache and merges the updated uRuns with the cached mSets.