Data Storage Copy Consistency via Verification Volume
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Solution Overview
Problem
In data storage systems, point-in-time copying can result in inconsistent data copies due to updates during the copying process, leading to potential corruption, and existing solutions rely on write restrictions and timers to maintain consistency, which may not guarantee a consistent state if the thaw operation is forgotten or delayed.
Innovation Solution
A data storage system with program logic that selects a verification volume to verify the write restriction status and allows resetting of the restriction, ensuring consistency by detecting a 'long busy' condition and allowing user-specified criteria for verification volume selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a write restriction (FREEZE) is applied to source data storage volumes during a copy operation to maintain consistency, then data consistency is improved, but write operations are blocked and system productivity deteriorates
Solution Approach 1:
The system performs preliminary verification by selecting a verification volume and checking its restriction status before allowing the thaw operation to proceed. This preliminary action ensures that the write restriction is properly in place before copying begins, preventing data consistency issues without needing to continuously block writes throughout the entire copy process.
Solution Approach 2:
The system implements feedback mechanisms where the verification volume's restriction status is continuously monitored and verified. The program logic responds to verification requests by checking the current restriction state, providing feedback on whether the write restriction remains in place, and allowing controlled thaw operations only when verification succeeds.
2Ease of operation
If a timer is used to automatically thaw volumes after a specified time to prevent forgotten thaw operations, then ease of operation is improved, but data consistency reliability deteriorates due to uncertainty about whether the group is consistent
Solution Approach 1:
The system uses feedback from verification requests to determine whether to allow thaw operations. Instead of relying solely on timers, the system continuously verifies the restriction status of the verification volume and only allows thawing when verification succeeds, ensuring data consistency is maintained while still providing automatic thaw functionality.
Solution Approach 2:
The system performs preliminary verification of the verification volume's restriction status before allowing any thaw operation to occur. This preliminary verification ensures that the write restriction is still in place and the data consistency group is properly formed before proceeding with thawing, eliminating uncertainty about consistency.
3Reliability
If verification of write restriction status is performed continuously to ensure data consistency, then data integrity is improved, but system complexity increases
Solution Approach 1:
The system extracts the verification function into a separate, dedicated mechanism using a verification volume and verification requests. This extraction isolates the complexity of continuous verification into a manageable subsystem that can be independently managed, while the main copy operation remains relatively simple.
Solution Approach 2:
The verification volume acts as an intermediary element that mediates between the write restriction mechanism and the thaw operation. By using this intermediary, the system can verify restriction status without directly complicating the main copy process, and the verification mechanism becomes a separate, manageable layer.
Data Source
AI summary
A data storage system which copies data from source data storage volumes to target data storage volumes restricts a write operation to at least one source data storage volume (FREEZE), to prevent the updating of a source while the data of a consistency group of interdependent data is being copied. Program logic selects a source data storage volume to which the restriction applies as a verification volume; and the program logic responds to a verification request to first employ the verification volume to verify that the restriction remains in place with respect to the verification volume, and to allow a reset of the restriction (THAW).