Rate Snooping in SAS Storage Networks
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Solution Overview
Problem
In storage network systems, rate thrashing occurs due to inconsistent link rates across network element pairs, leading to repeated speed negotiation and undesirable transitions into the SATA HOLD state, particularly in SAS topologies.
Innovation Solution
A method where speed negotiation is controlled to determine common link rates without activating the link, by transmitting initial data streams at various supported rates and withholding confirmation to prevent the storage network element from entering an active state, allowing the device to determine supported rates without completing the negotiation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If speed negotiation is performed independently for each network element pair, then each pair can achieve its highest commonly supported link rate, but rate inconsistency occurs across the storage network system leading to rate thrashing
Solution Approach 1:
The patent applies preliminary action by performing rate snooping during the COMINIT state before the link becomes active. The initiating device determines the supported link rates of the other device in advance by transmitting test data streams at different rates and analyzing the responses, storing this information for subsequent negotiation without causing rate thrashing
Solution Approach 2:
The patent implements feedback mechanisms where the initiating device transmits test data streams at various link rates during COMINIT state and receives response data streams from the other device. Based on the presence or absence of responses, the initiating device determines the supported link rates and uses this feedback information to establish a common rate that ensures consistency across all network element pairs
2Adaptability or versatility
If traditional SATA Port Selector is used in SAS topology, then speed negotiation can be performed, but the SATA Device is forced into SATA HOLD state causing operational problems
Solution Approach 1:
The patent segments the speed negotiation process into two distinct phases: rate snooping phase (during COMINIT state where test data streams are exchanged to determine supported rates) and active negotiation phase (after common rates are determined). This segmentation allows the SATA Device to remain in HOLD state during rate determination while enabling proper SAS topology operation without forcing the device into problematic SATA HOLD state transitions
Solution Approach 2:
The patent introduces rate snooping as an intermediary mechanism that operates during the COMINIT state before full link activation. This intermediary process allows the initiating device to gather information about the other device's supported link rates without requiring the other device to fully exit HOLD state, thus maintaining topology compatibility while avoiding operational problems
3Stability of the object's composition
If speed negotiation is re-initiated multiple times to achieve equivalent rates, then rate consistency can be achieved, but system performance degrades due to repeated negotiation overhead
Solution Approach 1:
The patent performs rate snooping during the COMINIT state as a preliminary action before formal speed negotiation begins. By determining the supported link rates of the other device in advance through test data stream exchanges and storing this information, the system avoids the need for multiple re-initiations of speed negotiation, thereby maintaining rate consistency while improving negotiation efficiency and reducing overhead
Data Source
AI summary
A method and apparatus for determining a set of common link rates for communication between two storage network elements in a storage network system. During the speed negotiation process, a controlling storage network element receives supported link rate information from a connected storage network element without providing any information in return. By not providing such information, although the speed negotiation process may not be completed, the controlling storage network element is still able to determine the supported link rates of the connected storage network element.