Snapshot Pair Creation in Active-Active Storage Replication
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Solution Overview
Problem
In synchronous replication configurations, creating identical point-in-time snapshots across active-active storage systems is challenging due to the need to suspend host IO operations and drain in-flight IOs, leading to increased IO latency and difficulties in detecting and correcting inconsistencies.
Innovation Solution
The technique involves creating corresponding snapshots on each storage system without suspending host IO operations or draining in-flight IOs, using asynchronous replication to transfer differential data and synchronize snapshots, allowing for efficient detection and correction of inconsistencies without performance impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional snapshot creation is used to ensure data consistency, then data consistency is improved, but IO latency increases significantly
Solution Approach 1:
The system performs preliminary actions by creating snapshots before actual consistency checking is needed. Snapshots are created continuously in the background, so when consistency issues arise, the snapshots are already available for immediate use, eliminating the need to suspend IO operations at the moment of consistency detection.
Solution Approach 2:
The patent enables continuous snapshot creation without interrupting host IO operations. By decoupling snapshot creation from IO suspension, the system maintains continuous useful action (IO processing) while simultaneously creating snapshots in the background, thus eliminating the trade-off between consistency and latency.
2Measurement precision
If host IO operations are suspended to create snapshots, then snapshot accuracy is improved, but storage system performance deteriorates
Solution Approach 1:
The system segments the snapshot creation process from the IO processing process. Instead of suspending all IO operations to create a snapshot, the system uses segmentation to allow IO operations to continue while capturing a consistent view of data through coordinated snapshot mechanisms, thus maintaining both accuracy and performance.
Solution Approach 2:
The patent introduces intermediary mechanisms (such as coordination between storage systems and hosts, or intermediate data structures) that enable snapshot creation without direct suspension of IO operations. These intermediaries facilitate the transfer of consistency information while IO operations continue processing data.
3Reliability
If in-flight IO operations are drained to create consistent snapshots, then data consistency is improved, but processing time increases
Solution Approach 1:
The system performs preliminary snapshot creation before consistency issues manifest. By continuously maintaining snapshots in the background, the system has ready-to-use consistent data views without needing to drain in-flight IO operations at the moment of consistency checking, thus reducing processing time.
Solution Approach 2:
The patent implements feedback mechanisms where storage systems continuously monitor replication status and snapshot availability. This feedback allows the system to detect inconsistencies and use pre-created snapshots for immediate correction, eliminating the need to wait for IO drain completion.
4Reliability
If synchronous replication is used to maintain data consistency, then data consistency is improved, but system complexity increases
Solution Approach 1:
The system uses copying mechanisms to create snapshots that replicate data states without requiring complex synchronous coordination. By copying data to snapshot structures independently on each storage system, the system achieves consistency without the complexity of full synchronous replication protocols.
Solution Approach 2:
The patent changes operational parameters by transitioning from strict synchronous replication to asynchronous snapshot creation with coordination. This parameter change allows the system to maintain consistency through snapshot synchronization rather than continuous synchronous data mirroring, reducing system complexity.
Data Source
AI summary
An apparatus includes at least one processing device, with the at least one processing device being configured, in conjunction with synchronous replication of at least one logical storage volume between first and second storage systems arranged in an active-active configuration, to create a first snapshot of the logical storage volume in the first storage system, to create a second snapshot of the logical storage volume in the second storage system, to create a third snapshot of the logical storage volume in the first storage system, to initiate an asynchronous replication cycle to transfer differential data between the first and the third snapshots in the first storage system to the second storage system, and to utilize the second snapshot and the transferred differential data to create an additional snapshot of the logical storage volume in the second storage system that is synchronized with the third snapshot in the first storage system.