Snapshot Migration in Storage Replication Using Replica Logs
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Solution Overview
Problem
Current data protection systems face challenges in seamlessly migrating user-generated snapshots across storage devices during storage federation, requiring efficient techniques to transfer snapshots and maintain data integrity across different storage arrays.
Innovation Solution
The method involves copying the oldest snapshot and associated log from a first storage array to a second array, generating snapshots, and applying data from the replica log until a bookmark is reached, ensuring data consistency and migration of snapshots between storage arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If snapshots are migrated between storage arrays during storage federation, then data protection and disaster recovery capabilities are improved, but data integrity and consistency may deteriorate due to data lag between source and target arrays
Solution Approach 1:
The patent applies preliminary action by copying the oldest snapshot first before initiating log application. This ensures that the base snapshot is available on the target array before applying incremental changes, preventing data integrity issues that would arise if logs were applied to a non-existent or incomplete snapshot foundation.
Solution Approach 2:
The patent uses copying to create a replica of the oldest snapshot on the target storage array. This copy serves as the foundation for subsequent log application, ensuring that the target array has an accurate starting point that matches the source array's snapshot state, thereby maintaining data integrity during migration.
2Productivity
If logs are copied and applied to migrate snapshots, then migration speed is improved, but system complexity increases due to the need to manage bookmarks and log application processes
Solution Approach 1:
The patent introduces bookmarks as intermediary markers within the log structure. These bookmarks denote specific snapshot points and serve as synchronization mechanisms between source and target arrays. The bookmarks simplify the complex task of tracking which log entries have been applied by providing clear, identifiable checkpoints that correspond to snapshot events.
Solution Approach 2:
The patent segments the log application process into discrete units marked by bookmarks. Instead of treating log application as a monolithic complex process, the system divides it into manageable segments between bookmarks, allowing for easier tracking, error handling, and resumption of migration operations without restarting the entire process.
3Adaptability or versatility
If multiple snapshots are maintained across storage arrays, then data recovery options are improved, but storage space requirements increase
Solution Approach 1:
The patent merges the storage requirements for multiple snapshots across different arrays by replicating only the oldest snapshot and then applying incremental log changes. This combining approach reduces the need to store complete copies of multiple snapshots simultaneously, as the target array can reconstruct historical states by applying logs to the copied snapshot, thereby reducing total storage space while maintaining recovery options.
Data Source
AI summary
In one aspect, a method includes copying an oldest snapshot of a first volume of a first storage array to a second volume of a second storage array and copying a log to the second storage array to form a replica log. The log includes write I/Os applied to the first volume and bookmarks denoting when snapshots of the first volume are generated. The method further includes generating a first snapshot of the second volume, applying data from the replica log to the second volume until a bookmark is reached and generating a second snapshot of the second volume after the bookmark is reached. The first snapshot is a copy of the oldest snapshot.