Storage Migration Metadata Consistency via Path Switching
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Solution Overview
Problem
Existing data migration techniques fail to properly transfer I/O state information, leading to operational issues in systems that rely on metadata for proper operation, especially in computer cluster configurations where state changes are based on I/O metadata.
Innovation Solution
A system that migrates data by creating new paths to the target storage device, transferring metadata in a platform-independent format, and setting the target device to accept I/O operations after metadata and data transfer, while rejecting I/O operations temporarily to ensure seamless migration and maintain state information consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is migrated from source storage device to target storage device, then data transfer is achieved, but I/O state information (metadata) is not properly transferred causing system operational failures
Solution Approach 1:
The system performs preliminary actions by creating new paths to the target storage device and setting it to accept I/O operations before completing the full metadata transfer. This allows the target device to be prepared and ready to receive state information, ensuring no information is lost during migration.
Solution Approach 2:
The patent uses an intermediary approach by implementing a path switching mechanism where new paths are created to the target storage device. These paths serve as intermediaries that allow I/O operations to be redirected while metadata transfer is in progress, ensuring continuous system operation and preventing information loss.
2Productivity
If I/O operations are continuously accepted during migration, then system availability is maintained, but data and metadata consistency may be compromised
Solution Approach 1:
The system dynamically adjusts the state of the target storage device during migration. It transitions through different states: initially accepting I/O operations to maintain availability, then temporarily rejecting operations to ensure consistency during metadata transfer, and finally resuming operations after consistency is verified. This dynamic state management resolves the contradiction between availability and consistency.
Solution Approach 2:
The migration process implements periodic action by alternating between accepting and rejecting I/O operations at specific intervals. The target device periodically switches between operational states to allow data transfer while maintaining consistency, ensuring both productivity and stability are achieved through rhythmic state transitions.
3Adaptability or versatility
If metadata transfer format is changed to platform-independent format, then migration compatibility is improved, but transfer complexity increases
Solution Approach 1:
The platform-independent format acts as an intermediary representation layer between the source and target storage devices. By converting metadata to this intermediate format during transfer, the system achieves broad compatibility across different platforms while managing complexity through a standardized conversion process rather than direct platform-specific transfers.
Data Source
AI summary
Determining whether to migrate from a source storage device to a target storage device includes determining if the target storage device is accessible by hosts that access the source storage device, determining if reservation information stored on the target storage device matches reservation information stored on the source storage device and migrating from the source storage device to the target storage device if the target storage device is accessible by hosts that access the source storage device and reservation information stored on the target storage device matches reservation information stored on the source storage device. Determining whether to migrate from a source storage device to a target storage device may also include, in response to initially determining that the reservation information stored on the target storage device does not match the reservation information stored on the source storage device, attempting to match the reservation information.