Online Data Migration Using Migration and Change Bitmaps
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Solution Overview
Problem
Existing data storage systems face challenges in performing online data copying and migration while ensuring data integrity and availability, particularly when source and target devices are online and accessible by hosts, as existing methods do not efficiently manage data synchronization and migration bitmaps to support concurrent operations.
Innovation Solution
A method and computer program product that utilize migration and change bitmaps to manage data copying and migration by updating bitmaps to indicate migrated and modified data tracks, allowing for incremental backups and online data migration by ensuring data is copied or migrated before performing read or write operations, and using these bitmaps to synchronize data between source and target devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data copying is performed offline (without host access), then data integrity is ensured, but device availability and host access are lost
Solution Approach 1:
The system performs preliminary actions by copying data blocks from source to target device before host access requests are made. The migration bitmap is pre-updated to reflect the copying status, enabling the system to serve host read requests from the target device even when source device data has been modified, thus maintaining both data integrity and device availability
Solution Approach 2:
The invention creates a copy of data blocks from the source device to the target device while maintaining a migration bitmap that tracks the copying status. This copying mechanism allows the system to provide consistent data to hosts while the source device remains accessible for modifications, resolving the contradiction between data integrity and device availability
2Ease of operation
If data copying is performed online (with host access), then device availability is maintained, but data synchronization and integrity become difficult to ensure
Solution Approach 1:
The migration bitmap serves as a feedback mechanism that continuously tracks which data blocks have been copied from source to target device. This feedback allows the system to determine whether to serve host read requests from the source or target device, ensuring data synchronization and integrity while maintaining device availability during online operations
Solution Approach 2:
The system performs preliminary data copying and updates the migration bitmap before host access requests are processed. This preliminary action ensures that when hosts access the target device, the data is already synchronized, maintaining both device availability and data integrity during online operations
3Reliability
If complete data recopying is performed, then data consistency is ensured, but time and resources are wasted
Solution Approach 1:
Instead of performing complete data recopying, the system uses the migration bitmap to identify only the specific data blocks that need to be copied. This partial action approach copies only the necessary portions of data, ensuring data consistency while significantly reducing the time and resources required compared to complete recopying operations
4Device complexity
If migration bitmap is not used, then system complexity is reduced, but data tracking and synchronization become inefficient
Solution Approach 1:
The migration bitmap is implemented as a simple binary copy of the source device's data block status. This lightweight copying mechanism efficiently tracks which data blocks have been migrated without adding significant system complexity, while dramatically improving data migration efficiency by enabling quick determination of copying status for any data block
Data Source
AI summary
Described are techniques for use with online data copying or migration. Data is pushed from a source to a target device while one or both of the source and target devices are available for use by one or more host systems. The host systems may perform I/O operations to the source and/or target devices while the data migration is ongoing if a copy session is defined on the data storage system(s) of the source and/or target devices. A copying operation performs data migration from the source to the target device. A migration vector is used to indicate which portions of the source have been migrated. A change vector may be associated with each of the source and/or target devices to indicate portions that have been modified in order to perform a differential copy operation.