SAS Switch Host Cache Data Evacuation
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Solution Overview
Problem
In SAS protocols, data trapped in a host cache module of a failed host controller cannot be efficiently transferred to storage, leading to potential storage inconsistency and complicating failover operations when a host controller fails.
Innovation Solution
A SAS switch with a communication manager and storage manager facilitates communication between host controllers and host cache modules using different communication channels, enabling direct data transfer from the failed host cache module to a replacement host cache module, allowing for automatic failover without manual intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data is stored in host cache module of failed host controller, then data transfer efficiency is improved during normal operation, but storage consistency deteriorates when host controller fails
Solution Approach 1:
The SAS switch acts as an intermediary device between the failed host controller and the storage system. It receives data from the host cache module of the failed controller through a second communication channel (management channel) and forwards it to the storage system, enabling data transfer without requiring the original host controller to be functional.
Solution Approach 2:
The communication between host controller and storage system is segmented into two independent channels: a first communication channel (SAS protocol) for normal data transfer, and a second communication channel (management channel) for cache data evacuation. This segmentation allows the management channel to operate independently when the primary controller fails.
2Reliability
If manual handling of host cache module is required during failover, then storage consistency can be maintained, but operational complexity and time increase
Solution Approach 1:
The SAS switch automatically detects host controller failures and initiates cache data evacuation to storage without requiring manual intervention. The system performs self-diagnosis and self-recovery by monitoring communication channels and automatically transferring cached data when failures are detected.
Solution Approach 2:
The system implements feedback mechanisms where the SAS switch continuously monitors the status of host controllers through communication channels. When a failure is detected, the switch receives feedback about the failed controller's cache status and automatically responds by evacuating data, creating a closed-loop failure recovery system.
3Reliability
If direct connection is established between initiator device and each target device, then data transfer reliability is improved, but device complexity and connection management difficulty increase
Solution Approach 1:
The SAS switch serves as an intermediary that manages connections between multiple initiator devices and target devices. Instead of requiring direct connections between each initiator and target, the switch centralizes connection management, reducing complexity while maintaining reliable data transfer through the fabric.
Data Source
AI summary
A SAS method to control host controller failure that includes, in response to receipt of a failure signal indicating that a host controller has failed, sending a wakeup signal to a host cache module of the failed host controller to cause the host cache module to determine whether there is trapped data in the host cache module that has not been transferred to a storage system. In response to receipt of a cache state signal indicating that there is trapped data in the host cache module that has not been transferred to the storage system, initiating transfer of the trapped data from the host cache module of the failed host controller to a host cache module of another host controller.