SAS RAID Controller Dual-Domain Architecture
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Solution Overview
Problem
SAS systems face issues with data availability due to intermittent failures of components like marginal PHYs, non-functional SAS cables, and entire SAS expanders, leading to communication errors and domain unavailability, which existing technologies fail to address effectively.
Innovation Solution
A system with two RAID controllers configured in an active-active failover manner, each with dual SAS initiators and a zoning SAS expander, creating two SAS domains to ensure continued access to disk drives even if one domain becomes non-functional, using an inter-controller SAS link to enable indirect access through the other RAID controller's expander.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single SAS domain is used to simplify the system structure, then device complexity is reduced, but data availability deteriorates when a component fails
Solution Approach 1:
The patent divides a single large SAS domain into multiple smaller SAS domains (first SAS domain and second SAS domain). Each domain is isolated and can operate independently, so when one domain fails due to component failures (marginal PHYs, bad cables, or expander failures), the other domains remain functional and maintain data availability.
2Reliability
If redundant paths are added to improve data availability, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent creates redundancy by adding a second dimension to the SAS topology through multiple domains. Instead of adding redundant paths within a single domain (which would increase complexity significantly), the system uses multiple independent domains where each domain provides an alternative access path to the same storage devices, achieving redundancy with manageable complexity.
3Reliability
If zone grouping is implemented to create multiple SAS domains, then data availability is improved through fault isolation, but expander configuration complexity increases
Solution Approach 1:
The patent applies different zone group configurations to different expanders based on their specific roles and connections. Each expander is configured with zone groups that are optimized for its local topology requirements, allowing flexible and targeted domain creation without requiring a uniform complex configuration across the entire system.
Data Source
AI summary
A storage system includes two RAID controllers, each having two SAS initiators coupled to a zoning SAS expander. The expanders are linked by an inter-controller link and create a SAS ZPSDS. The expanders have PHY-to-zone mappings and zone permissions to create two distinct SAS domains such that one initiator of each RAID controller is in one domain and the other initiator is in the other domain. The disk drives are dual-ported, and each port of each drive is in a different domain. Each initiator can access every drive in the system, half directly through the local expander and half indirectly through the other RAID controller's expander via the inter-controller link. Thus, a RAID controller can continue to access a drive via the remote path in the remote domain if the drive becomes inaccessible via the local path in the local domain.