SSD Host Memory Buffer Read-Ahead for Sequential Read Latency
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Solution Overview
Problem
Existing memory sub-systems face challenges in efficiently managing sequential read operations due to inherent delays in waiting for host read requests, which hinder responsiveness and throughput, and predictive caching strategies consume valuable cache resources without optimal resource utilization.
Innovation Solution
A memory controller that prefetches data from NAND memory components and stores it in a dedicated host memory buffer (HCB) without a specific request, allowing for faster read request servicing by providing pointers to prefetched data without accessing NAND components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the memory controller waits for host read requests before accessing NAND components, then cache resource usage is optimized, but read request servicing speed decreases
Solution Approach 1:
The memory controller performs preliminary action by prefetching sequential data from NAND components and storing it in the host memory buffer before the host actually requests it. The controller detects sequential read patterns and proactively loads the next expected data into the buffer, so when the host issues read requests, the data is already ready, eliminating waiting time and reducing latency.
2Productivity
If predictive caching strategies are used to prefetch data, then read request servicing is expedited, but cache resources are consumed
Solution Approach 1:
The host memory buffer acts as an intermediary between the NAND components and the host. Instead of the controller maintaining a large internal cache, it uses the host's existing memory buffer as a shared caching resource. This intermediary approach allows predictive caching to proceed without consuming valuable controller cache resources, while still enabling fast data delivery to the host.
Solution Approach 2:
The host memory buffer serves multiple functions: it acts as a cache for predictive data loading, a buffer for data transfer, and a memory resource that the host can access directly. By making the buffer universal for these purposes, the system avoids dedicated cache hardware and optimizes resource utilization across the entire system.
3Loss of time
If the controller stores prefetched data in host memory buffer, then read request latency is reduced, but device complexity increases
Solution Approach 1:
The memory controller implements self-service by automatically detecting sequential read patterns and initiating prefetch operations without explicit host commands. The controller monitors read requests, identifies sequential access patterns, and autonomously loads the next expected data into the host memory buffer, reducing the need for complex coordination between host and controller while still achieving low latency.
Data Source
AI summary
This disclosure pertains to a method for managing a memory sub-system that improves the efficiency of sequential data retrieval and storage. The methods utilize a host caching buffer (HCB), which is managed by the memory in a circular manner to ensure continuous data availability. The HCB dynamically adjusts to a multiples of the Maximum Data Transfer Size (MDTS) to maintain alignment with slot boundaries, facilitating orderly data management. The system's RAM used for the SSD read-ahead cache is released by the host after data transfer completion, optimizing resource utilization. The methods also include a pointer swap operation for subsequent read requests with prefetched data in the HCB, enhancing data access speed. These advancements provide a robust solution for managing memory sub-systems in computing environments, particularly beneficial for systems requiring efficient sequential data processing.