SAS Target Connection Management via Hardware Context Caching
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Solution Overview
Problem
Current data storage systems using serial storage protocols like SAS face inefficiencies in processing storage commands, particularly due to high latency and throughput limitations, as they often require CPU involvement for every command and struggle with temporary data under-runs and duplicate tags.
Innovation Solution
Implementing a hardware-implemented front-end in storage devices that pre-configures multiple connection contexts, caches recent connection contexts, estimates and prefetches data to prevent under-runs, and uses a hash table to detect duplicate tags, allowing for autonomous execution of storage commands and reducing CPU dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CPU involvement is required for every storage command processing, then connection management can be flexible and adaptive, but processing latency increases and throughput decreases
Solution Approach 1:
The patent segments connection management into two parts: common connection handling is done by hardware context caches, while exceptional cases are handled by CPU software. This segmentation allows most commands to be processed quickly in hardware without CPU involvement, improving throughput and reducing latency.
Solution Approach 2:
The patent implements pre-configured connection contexts in hardware that are prepared in advance. When a storage command arrives, the hardware can immediately use the pre-configured context without waiting for CPU processing, thereby reducing processing latency and increasing throughput.
2Productivity
If hardware pre-configures multiple connection contexts, then processing speed increases and CPU involvement decreases, but device complexity increases
Solution Approach 1:
The hardware context cache is designed to handle multiple connection contexts universally, allowing the same hardware structure to manage many different connections simultaneously. This multi-functionality improves throughput without proportionally increasing complexity.
Solution Approach 2:
The patent changes the parameter of connection context storage from software-managed to hardware-pre-configured, enabling faster processing. The context cache stores connection parameters in hardware, allowing rapid access and processing while maintaining manageable complexity through structured design.
3Loss of time
If connection contexts are cached in hardware, then processing latency reduces and throughput increases, but memory resources are consumed
Solution Approach 1:
The patent implements a partial caching strategy where only the most frequently used or recently used connection contexts are stored in the hardware context cache. This partial action approach reduces memory resource consumption while still achieving significant latency reduction for the majority of commands.
Data Source
AI summary
A method for data storage includes, in a storage device that communicates with a host over a storage interface for executing a storage command in a memory of the storage device, estimating an expected data under-run between fetching data for the storage command from the memory and sending the data over the storage interface. A data size to be prefetched from the memory, in order to complete uninterrupted execution of the storage command, is calculated in the storage device based on the estimated data under-run. The storage command is executed in the memory while prefetching from the memory data of at least the calculated data size.