SAS Expander Bridge for SATA Protocol Translation
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Solution Overview
Problem
The integration of SATA drives into a SAS domain is hindered by connectivity issues due to the single-user access nature of SATA drives and the inefficiencies of the Serial ATA Tunneling Protocol (STP), which adds complexity and cost to SAS expanders, and reduces the performance of the SAS domain.
Innovation Solution
A bridging functionality is implemented within existing SAS expanders, using a bridge embedded in or coupled to the expander, which translates between SAS and SATA protocols, and utilizes a routing table to route initiator requests and virtualize SATA devices as SSP targets, enhancing multi-initiator access and data transport efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple affiliations are created within a SAS expander for controlling access to SATA drives, then multi-initiator capability is provided, but technical complexity and implementation cost increase
Solution Approach 1:
A dedicated SAS/SATA bridge component is introduced as an intermediary between the SAS expander and SATA drives. The bridge handles protocol translation and access control, allowing the expander to remain simple while still providing multi-initiator capability to SATA drives through the bridging component.
Solution Approach 2:
The system is segmented into distinct functional components: the SAS expander handles SAS protocol routing, the SAS/SATA bridge handles protocol translation and SATA access control, and SATA drives provide storage. This segmentation allows each component to be optimized independently, reducing overall system complexity.
2Adaptability or versatility
If STP protocol is used for supporting SATA disks in SAS domain, then SATA drive compatibility is achieved, but data transport efficiency decreases due to half-duplex operation
Solution Approach 1:
The SAS/SATA bridge acts as an intermediary that receives full-duplex SAS signals from the expander, translates them to STP for SATA drives, and simultaneously translates STP responses back to SAS. This allows the SAS domain to maintain its efficient full-duplex operation while still supporting SATA drives.
Solution Approach 2:
The bridge component replaces the need for SATA drives to directly connect to the SAS expander, substituting the half-duplex STP mechanical connection with a full-duplex SAS connection that is translated to STP only at the bridge level, thereby improving data transport efficiency.
3Adaptability or versatility
If STP protocol is used for SATA drives, then protocol compatibility is provided, but implementation cost increases due to additional components needed in SAS expander
Solution Approach 1:
The SAS/SATA bridge is designed as a universal component that can be shared across multiple SATA drives and initiators. Instead of requiring each SATA drive to have dedicated expander components, a single bridge serves multiple functions, reducing implementation cost while maintaining protocol compatibility.
Solution Approach 2:
By introducing the bridge as a separate intermediary component rather than integrating STP support directly into the expander, the system achieves protocol compatibility without requiring expensive and complex expander modifications. The bridge handles all STP-related functionality externally.
Data Source
AI summary
Described herein is an improved mechanism for bridging between SAS and SATA drives based upon existing SAS expanders in a SAS domain. In particular, a bridge capable of translating between SAS and SATA protocols is embedded in or coupled to an expander. When a SAS initiator request is received at the expander, the expander can route the request, based on a routing table, either directly to a destination SAS device or to the bridge for necessary translation before it is transmitted to a destination SATA drive. The routing table includes corresponding relationships between all SAS addresses and Phys through which those SAS and SATA devices are attached to the expander. SATA devices can be virtualized in the expander through a few assigned addresses in the routing table in a SAS discovery process.