Fast Context Switching Across Remote Expanders

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Solution Overview

Problem

In storage topologies, the connection overhead penalty is significant, especially with multiple cascaded expanders, as existing Fast Context Switching (FCS) protocols only allow for connection reuse between end devices directly attached to the same expander, limiting the reuse or expansion of connections to end devices connected to remote expanders.

Innovation Solution

Enhancements to the FCS protocol enable an initiator to reuse or extend existing connections by instructing all expanders in the connection path to monitor for a SWITCH_ADDRESS_FRAME, allowing for the reuse or expansion of connections between an initiator and end devices attached to different expanders, thereby optimizing connection switching and reducing overhead.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If existing Fast Context Switching (FCS) protocols are used for connection switching, then connection switching speed is improved for end devices directly attached to the same expander, but connection overhead penalty increases significantly for end devices attached to remote expanders

Engineering Contradiction:

Improveconnection switching speedVSAvoidconnection overhead penalty

Core Design Contradiction:

SpeedVSLoss of time

Solution Approach 1:

The enhanced FCS protocol enables expanders to perform multiple functions: they not only switch connections for locally attached end devices but also extend and reuse connections for remotely attached end devices. The SWITCH_ADDRESS_FRAME mechanism allows a single frame to trigger connection actions across multiple expanders in the path, making the system universally applicable to both local and remote end devices.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The protocol performs preliminary actions by having expanders monitor for SWITCH_ADDRESS_FRAME frames in advance. When a frame is received, the expanders are already configured to reuse or extend existing connections without requiring full re-establishment, thus reducing the connection overhead penalty before data transmission begins.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If connections are established through multiple cascaded expanders, then connectivity to remote end devices is achieved, but connection overhead penalty becomes more pronounced

Engineering Contradiction:

Improveconnectivity to remote end devicesVSAvoidconnection overhead penalty

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent merges the connection establishment process with the connection switching process. By combining the reuse of existing connections with the switching mechanism, the system achieves both connectivity to remote end devices and reduced overhead. The SWITCH_ADDRESS_FRAME frame combines switching instructions with connection reuse/extension commands for all expanders in the path.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The SWITCH_ADDRESS_FRAME acts as an intermediary mechanism that coordinates connection actions across multiple expanders. This frame serves as a mediator to instruct each expander in the path to reuse or extend existing connections, thereby achieving remote connectivity without the full overhead of traditional connection establishment.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of time

If existing connections are reused for remote end devices, then connection overhead time is reduced, but protocol complexity increases

Engineering Contradiction:

Improveconnection overhead timeVSAvoidprotocol complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The expanders perform self-service by automatically monitoring for SWITCH_ADDRESS_FRAME frames and autonomously deciding to reuse or extend existing connections. The protocol leverages the existing connection state information stored at each expander, allowing them to make intelligent decisions without external control, thus reducing overhead while managing complexity through localized intelligence.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The protocol changes the state parameters of connections by transitioning from purely new connection establishment to reuse/extension modes. The SWITCH_ADDRESS_FRAME mechanism changes the connection state from unclosed to reusable, allowing the system to leverage existing parameters (paths, configurations) rather than creating new ones, thereby reducing overhead.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9043529B2Method to facilitate fast context switching for partial and extended path extension to remote expanders

Publication Date: 2015.05.26 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

A method, apparatus, and system for switching from an existing target end device to a next target end device in a multi-expander storage topology by using Fast Context Switching. The method enhances Fast Context Switching by allowing Fast Context Switching to reuse or extend part of an existing connection path to an end device directly attached to a remote expander. The method can include reusing or extending at least a partial path of an established connection between an initiator and the existing target end device for a connection between the initiator and the next target end device, whereby the existing target end device and the next target end device are locally attached to different expanders.