Switch Mediator for Slow Drain Primitive Notification in Fibre Channel
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Solution Overview
Problem
In Fibre Channel networks using credit-based flow control, a slow drain condition can persist due to the inability to send a message to the target when there are no available credits, hindering network performance as the target never receives a slowdown message.
Innovation Solution
A switch detects a slow drain situation and sends a slow drain primitive to the affected device, which then sends a throttling message to the source, utilizing a primitive signal that does not consume credits, allowing notification even when credits are unavailable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If credit-based flow control is used in Fibre Channel networks, then flow control is achieved, but the ability to notify slow drain conditions is lost when credits are depleted
Solution Approach 1:
The patent introduces a switch as an intermediary device between the target and sources. The switch monitors credit consumption and detects slow drain conditions, then generates and sends R_RDY primitives to notify the target. This intermediary approach allows condition notification without requiring the target to send frames back to sources, thus resolving the contradiction between maintaining flow control and preserving notification capability.
2Productivity
If the target sends slow down messages to sources, then sources are notified to slow down, but this requires available credits which may not exist in slow drain conditions
Solution Approach 1:
The switch acts as a mediator that detects slow drain conditions by monitoring credit consumption patterns and generates R_RDY primitives to notify the target device. This eliminates the need for the target to send frame-based slow down messages that would require available credits. The switch's monitoring and notification mechanism operates independently of credit availability, allowing productivity maintenance without requiring additional credits.
Solution Approach 2:
The patent implements a feedback mechanism where the switch continuously monitors the credit consumption rate at the target and compares it against the frame transmission rate. When a slow drain condition is detected (credit consumption falls below a threshold), the switch provides feedback by sending R_RDY primitives to the target, which then notifies sources to slow down. This feedback loop operates without consuming additional credits from the target, resolving the contradiction between maintaining network productivity and preserving credit quantity.
3Loss of information
If frames are used to communicate slow drain conditions, then messages can be sent, but this consumes credits that may already be depleted
Solution Approach 1:
The switch serves as an intermediary that generates R_RDY primitives to communicate slow drain conditions to the target device. These R_RDY primitives are generated and sent by the switch rather than requiring the target to send frames back to sources. This approach preserves condition notification capability while avoiding the consumption of credits at the target device, as the notification mechanism is decoupled from the target's credit availability.
Data Source
AI summary
A switch detecting a slow drain situation and providing a slow drain primitive to the slow draining device, such as a storage unit. The slow draining device detects the slow drain primitive and provides a throttling message to the relevant sources of frames being received by the slow draining device. The use of a primitive instead of a frame allows the slow condition notification to be provided even when there is no available credit for sending a frame.