Non-Host Data Migration Using Write Protection
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Solution Overview
Problem
Conventional data storage system migration methods face issues with data corruption due to mirroring and incomplete shutdown of applications, leading to potential data inconsistency and corruption, especially when host-based migration is slow and resource-intensive.
Innovation Solution
Implementing non-host-based migration by initially setting the target LUN to a write-protected state, ensuring all applications are shut down before allowing write access, and then performing an online migration while applications continue to run, with the target system managing access to prevent data corruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the target LUN is made accessible to hosts with the same signature as the source LUN, then the migration can proceed, but data corruption occurs due to accidental mirroring by host drivers
Solution Approach 1:
The patent applies preliminary anti-action by making the target LUN inaccessible to hosts before the migration is complete. Specifically, the target LUN is not presented to hosts until the source LUN has been fully copied, preventing host drivers from mistakenly mirroring data between the two LUNs. This preemptive measure eliminates the data corruption risk before it can occur.
Solution Approach 2:
The patent implements preliminary action by copying the entire source LUN to the target LUN before making the target accessible to hosts. The migration process completes the bulk copy operation first, ensuring data integrity, and only then presents the target LUN to hosts for normal operation.
2Reliability
If host-based migration is used to avoid data corruption, then data integrity is maintained, but host processing power is consumed and migration speed decreases
Solution Approach 1:
The patent extracts the migration management function from the host system and places it entirely on the storage system side. The storage system autonomously performs the bulk copy operation and manages LUN accessibility, removing the burden of host-based migration management. This eliminates host processing overhead while maintaining data integrity through proper access control.
Solution Approach 2:
The storage system acts as an intermediary that manages the migration process between source and target LUNs without host involvement. The storage system controls when hosts can access the target LUN, mediating the migration process to ensure data integrity while freeing host resources for other tasks.
3Reliability
If applications are shut down before migration to prevent data corruption, then data consistency is maintained, but application downtime increases
Solution Approach 1:
The patent performs the data copying action in advance by completing the bulk copy of the source LUN to the target LUN before making the target accessible to hosts. This preliminary data transfer ensures that when applications are redirected to the target LUN, they immediately access complete and consistent data without requiring application shutdowns during the migration process.
Data Source
AI summary
Techniques are presented for implementing non-host-based migration in a manner that is not subject to certain types of data corruption. This may be accomplished by preventing any hosts from having write access to a target LUN until it can be confirmed that all applications that access a source LUN have been shut down. This arrangement prevents accidentally writing to the target LUN while the source LUN is still being accessed. As a further precaution, just in case the confirmations are incorrect, a target data storage system can direct a source data storage system to remove access to the source LUN from all of the hosts, which has a similar effect. The migration can then proceed.