SAS Expander Open Address Frame Cut-Through Processing
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Solution Overview
Problem
Current SAS expander devices process open address frames using a store-and-forward operation, which serializes each step and does not take advantage of parallelization, leading to increased connection setup time delays in SAS networks.
Innovation Solution
Implementing a cut-through operation in both the source PHY and the expander connection manager (ECM) to allow parallel processing of open address frame steps, such as asserting an open request and performing address lookup while the frame is still being received, and completing CRC checks and arbitration after the entire frame is received.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If store-and-forward operation is used to process open address frames, then processing completeness is ensured, but connection setup time delay increases
Solution Approach 1:
The patent applies preliminary action by initiating the open request assertion and address lookup processes before the entire open address frame is received. The source PHY asserts an open request to the ECM as soon as the frame type is identified, and the ECM begins address lookup while the frame data is still being transferred. This allows processing to start in advance rather than waiting for complete frame reception, thereby reducing connection setup time while ensuring processing completeness through subsequent CRC verification.
2Reliability
If store-and-forward operation is used, then data integrity is maintained, but processing throughput decreases
Solution Approach 1:
The patent enables parallel processing operations by initiating data lookup and open request assertion before complete frame reception. The ECM performs address lookup in parallel with the ongoing frame transfer from source PHY to destination PHY, and the arbitration process can begin while remaining frame data is still being received. This preliminary and parallel processing significantly increases throughput while maintaining data integrity through final CRC check verification.
Solution Approach 2:
The patent implements continuity of useful action by ensuring that processing operations continue without idle waiting periods. While frame data is being continuously transferred, the ECM continuously performs address lookup and the source PHY continuously asserts open requests. This eliminates idle time between frame reception and processing, maximizing productivity while maintaining data integrity through uninterrupted processing streams and final verification.
Data Source
AI summary
SAS expanders are commonly used within a SAS network topology to allow multiple disk drives (targets) to connect to multiple host devices (initiators). A connection between an initiator and a target is setup inside an expander on the pathway between the initiator and the target. A source device sends a connection request message called an open address frame using in-band signaling. The expander processes the open address frame and forwards an modified open address frame to the next expander in the path or to the final destination device.