SAS Expander Path Selection for Storage Latency
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Solution Overview
Problem
In storage systems with a large number of SAS expanders, the latency introduced by the expander sequence significantly impacts the performance of high-response-speed storage devices when they are connected later in the sequence, leading to deteriorated performance for command issuers.
Innovation Solution
A storage system that selects an optimal path with fewer expanders for command transmission to high-response-speed storage devices, reducing latency by preferring paths with fewer intervenient expanders over roundabout paths with more expanders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of expanders in the expander sequence is increased to support more storage devices, then the storage system capacity is improved, but the latency for command transmission to high-response-speed storage devices is increased
Solution Approach 1:
The system dynamically selects between optimal and roundabout paths based on the response speed characteristics of the target storage device. High-response-speed devices (SSDs) are routed through the optimal path with fewer expanders to minimize latency, while lower-response-speed devices (HDDs) can use either path without significant performance impact. This dynamic path selection resolves the contradiction by adapting the expander sequence length to the specific performance requirements of each storage device.
2Quantity of substance
If high-response-speed storage devices are connected to expanders in later stages of the expander sequence, then storage system capacity is improved, but the performance of these storage devices is deteriorated due to increased latency
Solution Approach 1:
The system performs preliminary identification of the target storage device's response speed characteristics before command transmission. Based on this pre-assessment, the initiator device selects the appropriate path (optimal or roundabout) in advance. This preliminary action ensures that high-response-speed devices are always routed through the optimal path with fewer expanders, preventing performance deterioration while maintaining the ability to connect storage devices at any position in the expander sequence.
3Loss of time
If the optimal path with fewer expanders is selected for high-response-speed storage devices, then command transmission latency is reduced, but the system complexity increases due to path selection requirements
Solution Approach 1:
The system uses response speed as a key parameter to determine path selection. By categorizing storage devices based on their response speed characteristics (high-response-speed vs. lower-response-speed), the system simplifies the path selection logic. High-response-speed devices trigger selection of the optimal path, while other devices can use default paths. This parameter-based approach reduces complexity compared to evaluating all possible path combinations.
Data Source
AI summary
A storage system includes an expander sequence including a plurality of expanders coupled in series, a plurality of storage devices coupled to the expander sequence, first and second initiator devices coupled to the expander sequence, and a processor. The processor selects an optimal path, with respect to a transmission destination device of a command among the plurality of storage devices and the plurality of expanders, between the optimal path which is an initiator device with fewer expanders in a distance to the transmission destination device and a roundabout path which is an initiator device with more expanders in a distance to the transmission destination device, and transmits the command to the transmission destination device through the selected optimal path.