Host Interface Spoofing for Redundant Storage Failover
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Solution Overview
Problem
Systems like those from IBM Corporation are not inherently capable of configuring separate physical storage devices as a single logical device, which prevents redundant storage configurations that mimic host-to-storage device coupling errors.
Innovation Solution
The system accesses at least two separate physical storage devices as a single logical device by receiving data/metadata from both devices and spoofing it to appear as if it is coming from only one device, allowing metadata to be directed and forwarded between them using a data link, effectively revising storage device identifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate physical storage devices are configured as a single logical device for redundant storage, then system reliability is improved through automatic failover, but system complexity increases due to the need for spoofing mechanisms and metadata management
Solution Approach 1:
A host interface unit acts as an intermediary between the host system and multiple storage devices. It receives I/O commands from the host, determines which storage device should handle each command based on device status, and manages metadata exchange between storage devices. This intermediary approach enables redundant storage configuration without requiring the host system itself to be complex.
Solution Approach 2:
The system creates a logical copy of storage device identity through spoofing mechanisms. When one storage device is unavailable, the host interface unit can present data from another storage device with modified identifiers that make it appear as if the original device is responding. This copying approach maintains system reliability while managing complexity at the interface level rather than requiring fundamental system redesign.
2Adaptability or versatility
If storage device identifiers are spoofed to make separate devices appear as a single logical device, then adaptability is improved for redundant storage configurations, but measurement precision deteriorates as the system can no longer distinguish between actual and spoofed device identities
Solution Approach 1:
The system adds a logical dimension to storage device identification by introducing virtual device identifiers that exist separately from physical device identities. The host interface unit maintains mapping between physical device identifiers and virtual identifiers, allowing the system to adapt to different storage configurations (single device, redundant devices, failed devices) while preserving the ability to precisely track actual device states through the mapping layer.
Solution Approach 2:
The identification system combines multiple layers: physical device identifiers, virtual device identifiers, and status indicators. This composite identification approach allows the system to present a unified logical device identity to the host while maintaining precise tracking of individual physical device states through the combined identifier system.
3Productivity
If metadata is directed and forwarded between storage devices using a data link, then productivity is improved through automatic failover without manual intervention, but loss of information increases due to potential metadata corruption or loss during transmission
Solution Approach 1:
The host interface unit implements feedback mechanisms where storage devices send status information and metadata acknowledgments back to the interface unit. The interface unit tracks metadata transmission states, detects errors or losses in metadata communication, and can request retransmission or switch to backup storage devices. This feedback approach enables automatic failover while minimizing metadata loss through error detection and correction.
Data Source
AI summary
Accessing at least two separate physical storage devices as a single logical device includes receiving data/metadata from both of the separate physical storage devices and causing the data/metadata to appear to be coming from only one of the storage devices by spoofing data/metadata from at least one of the storage devices to appear to be coming from the other of the storage devices. Spoofing data/metadata may include revising storage device identifiers. The storage device identifiers may include serial numbers and port identifiers.