Pipelined Read Optimization for SSD Cache Storage Systems
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Solution Overview
Problem
Traditional storage systems face challenges in balancing cost and performance when integrating SSDs as a caching layer, particularly in limiting write-erase cycles to extend SSD lifespan and improving read access latency while ensuring fault tolerance.
Innovation Solution
The integration of SSDs as a caching layer with a write-evict unit (WEU) structure that limits write-erase cycles and employs a Merkle tree file structure for efficient data management, allowing for parallel data retrieval from SSD and persistent storage units, and includes mechanisms for fault tolerance by invalidating failed data blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SSDs are integrated as a caching layer to improve read access latency, then read performance is improved, but write-erase cycles increase which reduces SSD lifespan
Solution Approach 1:
The patent changes the parameter of data organization by implementing a write-evict unit structure that groups data into fixed-size units. This allows the system to track and limit write operations at the unit level rather than individual block level, thereby controlling write-erase cycles while maintaining fast read access through SSD caching.
Solution Approach 2:
The patent introduces a cache management system as an intermediary between the host and SSD cache layer. This intermediary implements policies to manage write operations, track write-erase cycles, and coordinate with persistent storage, thereby protecting the SSD from excessive write operations while maintaining caching performance.
2Speed
If SSD cache is used to improve read performance, then read access latency decreases, but system complexity increases due to cache management requirements
Solution Approach 1:
The patent segments the cache into fixed-size write-evict units with standardized structures containing metadata and data portions. This segmentation simplifies management by providing uniform units for tracking, allocating, and evicting data, reducing the complexity of cache management operations.
Solution Approach 2:
The patent changes the organizational parameter of cache data from arbitrary blocks to fixed-size write-evict units with defined structures. This standardization simplifies management logic by providing consistent unit sizes and metadata formats, making cache operations more predictable and easier to manage.
3Reliability
If data is replicated to primary system for backup, then fault tolerance is improved, but read access latency increases due to storage system latency
Solution Approach 1:
The patent introduces an SSD-based cache layer as an intermediary between persistent storage and the primary system. This cache layer provides fast read access to frequently accessed data while maintaining fault tolerance through replication, thereby reducing read latency without sacrificing reliability.
Solution Approach 2:
The patent applies local quality by placing frequently accessed data in the SSD cache layer closer to the processor, while less frequently accessed data remains in persistent storage. This creates a hierarchical structure where hot data benefits from fast local access while cold data maintains fault tolerance in persistent storage.
Data Source
AI summary
According to some embodiments, a backup storage system receives a request from a client at a storage system for accessing data segments. For each of a first groups of the data segments requested that are stored in a solid state device (SSD) cache, the system requests a first batch job for each of the first groups to retrieve the first groups of the data segments from the SSD cache via a first set of input/output (IO) threads. For each of a second groups of the data segments requested that are not stored in the SSD cache, the system requests a second batch job for each of the second groups to retrieve the second groups of the data segments from storage units of the storage system via a second set of input/output (IO) threads. The system assembles received segments and returns them to the client altogether.