SAS Expander Topology for RAID Storage Expansion

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Solution Overview

Problem

Existing data storage systems, particularly RAID systems, face challenges in expanding storage capacity to meet growing business needs without compromising fault tolerance and performance.

Innovation Solution

The implementation of a data storage system with a pair of SAS expanders, storage processors, and multiplexers in two chassis configurations, allowing for the expansion of disk drives and increased storage capacity while maintaining fault tolerance and performance through bidirectional ports and expansion ports.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If storage capacity is expanded by adding more disk drives, then storage capacity increases, but system complexity increases

Engineering Contradiction:

Improvestorage capacityVSAvoidsystem complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The system is divided into multiple independent chassis, each containing a pair of SAS expanders and associated disk drives. This segmentation allows storage capacity to be expanded by simply adding more chassis modules without increasing the complexity of individual chassis units. Each chassis operates as a self-contained expansion unit with dedicated expanders and multiplexers.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The SAS expanders are designed with universal bidirectional ports that can interface with both single-port and dual-port disk drives. The expanders can function in multiple configurations (single expander mode or paired expander mode) depending on the storage capacity requirements. This multi-functionality allows the same hardware architecture to support varying storage capacities without requiring different system designs.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Quantity of substance

If storage capacity is expanded by adding more disk drives, then storage capacity increases, but connectivity requirements increase

Engineering Contradiction:

Improvestorage capacityVSAvoidconnectivity

Core Design Contradiction:

Quantity of substanceVSAdaptability or versatility

Solution Approach 1:

The SAS expanders are designed with universal bidirectional ports that can interface with both single-port and dual-port disk drives. This universality ensures that the system can accommodate various drive configurations without requiring different connectivity solutions, thereby expanding storage capacity while maintaining adaptable connectivity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

Multiplexers are introduced as intermediary devices between the SAS expanders and disk drives. These multiplexers manage the connectivity between expanders and drives, allowing a single expander port to efficiently serve multiple drives through time-division multiplexing. This intermediary layer simplifies connectivity requirements by reducing the number of direct expander-to-drive connections needed.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If fault tolerance is maintained through redundant components, then reliability improves, but device complexity increases

Engineering Contradiction:

Improvefault toleranceVSAvoidcomponent redundancy

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system uses paired SAS expanders in each chassis, where each expander can operate independently or in conjunction with the other. This segmentation of redundant components into modular units allows fault tolerance to be achieved without creating a monolithic complex system. If one expander fails, the other can continue to operate, maintaining system reliability while keeping the redundancy manageable through clear modular boundaries.

Inventive Principle:

Principle #1Segmentation

4Productivity

If performance is maintained during expansion, then system performance is preserved, but system complexity increases

Engineering Contradiction:

Improvesystem performanceVSAvoidexpansion architecture

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

By segmenting the storage system into independent chassis modules, each with dedicated SAS expanders and multiplexers, the system maintains performance isolation. Expansion operations in one chassis do not impact the performance of other chassis, allowing performance to be preserved while enabling straightforward capacity expansion through simple module addition.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS7574542B2SAS expansion topology for RAID data storage including multiplexers and SAS expanders for interfacing with single or dual ports drives

Publication Date: 2009.08.11 EMC IP HLDG CO LLC

AI summary

A data storage system having a first chassis, such first chassis having a pair of SAS expanders and a second chassis having a pair of SAS expanders. The first one of the pair of SAS expanders is connected to only an expansion port of a first one of a pair of signal processor printed circuit boards in the first one of the chassis. An expansion port of a second one of the pair of SAS expander is connected to only the expansion port of a second one of the pair of signal processor printed circuit boards in the second one of the chassis.