Storage Virtualization Subsystem Host-Side Redundancy via SAS
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Solution Overview
Problem
The challenge is to maintain data accessibility and redundancy on the host side when using SAS connectivity, as the peer-to-peer connection characteristic of SAS does not provide multiple device IDs, making it difficult for the surviving controller to inherit the identity of a failed controller, thereby ensuring continuous data access.
Innovation Solution
A storage virtualization subsystem with host-side redundancy is implemented using a SVC pair, SAS expanders, and a PSD array, where each SVC has built-in virtual SAS expanders or a switch component to provide multiple virtual IDs, ensuring that the surviving controller can take over the identity and operations of the failed controller without disrupting the initiator's access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SAS connectivity is used with peer-to-peer connection characteristic, then connection simplicity and speed are improved, but the ability to provide multiple device IDs is lost, making it difficult for the surviving controller to inherit the identity of a failed controller
Solution Approach 1:
The patent introduces an intermediary mechanism (virtual device ID mapping layer) between the SAS controller and the host system. This intermediary allows the surviving controller to translate its own device ID into the original device ID of the failed controller, enabling identity inheritance without changing the underlying SAS peer-to-peer connection structure. The intermediary layer handles the complexity of ID mapping while preserving the simplicity of SAS connectivity.
Solution Approach 2:
The patent segments the device identification function from the physical connection layer. By separating the logical device ID from the physical SAS connection, the system allows multiple virtual device IDs to be associated with a single physical SAS interface. This segmentation enables the surviving controller to present multiple virtual IDs through the same SAS connection, solving the identity inheritance problem while maintaining connection simplicity.
2Device complexity
If a single SVC is used, then device complexity is reduced, but redundancy and fault tolerance are lost
Solution Approach 1:
The patent merges the functionality of multiple SVCs into a single controller by implementing virtual device ID mapping and identity inheritance capabilities. The single SVC can assume the identity of multiple potential failed controllers, effectively combining the redundancy function of multiple controllers into one. This reduces device complexity while maintaining fault tolerance through the virtualization and identity mapping mechanisms.
3Device complexity
If the surviving SVC cannot inherit the identity of the failed controller, then device complexity is reduced, but data accessibility and continuous operation are compromised
Solution Approach 1:
The patent implements a virtual copy mechanism where the surviving controller creates a virtual copy of the failed controller's device ID and presentation to the host system. Through virtual device ID mapping, the surviving controller can present itself as the original failed controller, allowing the host system to continue accessing data without detecting any change. This copying approach maintains data accessibility while managing identity complexity through virtualization.
Data Source
AI summary
This invention discloses a storage visualization subsystem and system with host-side redundancy via SAS connectivity. The I/O interconnect interface between the storage visualization controller and the host is a serial-attached SCSI (SAS) interface. At least one SAS expander is inserted on the I/O interconnect path of the host side to provide the function of device expansion. Or, a built-in virtual SAS expander is disposed inside the storage virtualization controller to provide multiple virtual IDs for each SAS port. When one controller in the storage virtualization controller pair malfunctions or fails, the invention provides solutions in accord with different embodiments so that the surviving controller can inherit the ID of the failed one. Thus, the host can keep functioning normally as it is not aware of any change in the device status.