Storage Volume Migration Using Snapshot-Based Copy Pair Switching
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Solution Overview
Problem
Existing volume migration techniques in storage systems require suspending I/O requests from hosts during the migration process, disrupting user work.
Innovation Solution
A method for migrating volumes between storage nodes by creating a snapshot of the source volume, deleting the existing pair relationship, migrating the volume while continuing I/O processing, and establishing a new pair relationship post-migration, with difference data identification and application to maintain continuous I/O operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a volume copy pair is created between storage controllers and journal switching is performed during migration, then data consistency is maintained, but I/O requests from hosts must be suspended
Solution Approach 1:
The patent applies preliminary action by creating a snapshot of the source volume before initiating the migration process. This snapshot captures the data state at a specific point in time, allowing the migration to proceed using this static copy while the original volume continues to accept I/O operations. The snapshot is created in advance of the actual data transfer, enabling uninterrupted host operations during migration.
Solution Approach 2:
The patent uses copying by creating a snapshot (a copy of the volume data) rather than migrating data directly from the live source volume. This copy allows the migration process to work with a static data set while the original volume remains operational. The snapshot copy serves as the migration source, eliminating the need to suspend I/O requests on the production volume.
2Reliability
If journal switching is performed to maintain data consistency during volume migration, then data integrity is preserved, but user work related to host I/O is affected
Solution Approach 1:
The snapshot is created in advance of the migration process, capturing the volume state before any data transfer begins. This preliminary action allows the migration to proceed independently of ongoing I/O operations, maintaining data integrity without interrupting user work. The journal switching that would normally be required is eliminated because the snapshot provides a consistent starting point for migration.
Solution Approach 2:
The snapshot acts as an intermediary between the source volume and the migration process. Instead of directly migrating data from the live volume (which would require journal switching and I/O suspension), the migration process uses the snapshot as an intermediate data source. This intermediary allows uninterrupted I/O operations on the original volume while enabling seamless data transfer from the snapshot.
3Reliability
If volume migration is performed with traditional journal switching, then data consistency between source and destination is ensured, but migration time and host I/O suspension are increased
Solution Approach 1:
By creating the snapshot before migration begins, the system establishes a consistent data baseline in advance. This preliminary action eliminates the need for time-consuming journal switching operations during the migration process itself. The migration can proceed directly from the snapshot without pausing to perform journal switches, significantly reducing total migration time while maintaining data consistency.
Solution Approach 2:
Using the snapshot copy as the migration source allows the process to bypass the complex journal switching mechanism entirely. The copy provides a stable, consistent data set that can be transferred without interruption or time loss. This copying approach eliminates the sequential overhead of journal switching, reducing migration time while ensuring data consistency between source and destination volumes.
Data Source
AI summary
In a system including a first storage system and a second storage system, there is a pair relationship of an copy between a first volume of the first storage system and a second volume of the second storage system. The system sets the second volume as a migration target and creates a copy volume of the second volume in another storage node of the second storage system. Difference data between the first volume and a snapshot of the first volume is reflected in the copy volume. A pair relationship of an copy is newly created between the first volume and the copy volume such that data related to an I/O request from a host to the first volume is reflected in the copy volume.