Storage Data Migration Metadata Mapping
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Solution Overview
Problem
Existing data migration methods require significant data to pass through the host processor, which can be impractical due to data volume and may disrupt host operations during storage device replacement, while maintaining disaster recovery capabilities.
Innovation Solution
The system migrates data from a first storage device to a second by modifying metadata to change the mapping of logical devices to physical devices, allowing independent data transfer without host involvement, and acknowledges writes only after data is successfully written to both devices, enabling seamless transition and disaster recovery without host intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is migrated by having the host read from the old storage device and write to the new storage device, then the migration can be performed, but a significant amount of data passes through the host which may be impractical due to data volume and may disrupt host operations
Solution Approach 1:
The patent extracts the data migration function from the host processor by implementing direct storage-to-storage data transfer. The host is removed from the data path during migration operations, allowing bulk data transfer without consuming host resources or disrupting host operations. This resolves the contradiction by maintaining disaster recovery capability through automated migration while preserving host productivity.
Solution Approach 2:
The patent introduces an intermediary data migration controller that mediates between the old and new storage devices. This controller handles the data transfer independently of the host, enabling asynchronous migration that does not interfere with host operations. The intermediary maintains data consistency and disaster recovery positioning without requiring host involvement in the actual data transfer.
2Productivity
If data is migrated independently of host I/O operations, then host operations are not disrupted, but it becomes challenging to maintain synchronized data and disaster recovery position
Solution Approach 1:
The patent implements a feedback mechanism where the data migration controller continuously monitors host I/O operations and adjusts the migration process accordingly. When the host performs write operations, the controller detects these changes and synchronizes the new storage device to maintain data consistency. This feedback loop ensures disaster recovery positioning is maintained without requiring the host to participate in migration operations.
Solution Approach 2:
The patent performs preliminary data copying from the old storage device to the new storage device before the host needs to access the migrated data. This advance preparation ensures that by the time the host requires data from the new storage device, the data is already synchronized and ready, maintaining both host productivity and disaster recovery capability.
3Reliability
If the host acknowledges write operations only after data is written to both storage devices, then data consistency is ensured, but this may increase the time for write operations
Solution Approach 1:
The patent performs preliminary data copying to the new storage device in advance, before the host needs to acknowledge the write operation. By pre-synchronizing data during idle periods or in parallel with host operations, the system reduces the time penalty for consistency checking. The host can acknowledge writes more quickly because the heavy lifting of data transfer has already been completed or is in progress independently.
Data Source
AI summary
Migrating data from a first storage device to a second storage device includes causing all data of the first storage device to be copied from the first storage device to the second storage device and causing the host computer to transition from performing I/O operations with the first storage device to performing I/O operations with the second storage device by modifying metadata used for I/O operations to change a mapping of logical devices to physical devices only after causing all data of the first storage device to be copied from the first storage device to the second storage device. Migrating data from the first storage device to the second storage device is independent of any I/O operations by the host. A data write operation from the host is acknowledged only after the data has been successfully written to both the first storage device and the second storage device.