Storage Resynchronization Using Dirty Region and Metadata Logs
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Solution Overview
Problem
Existing methods for transitioning from asynchronous replication to synchronous replication in storage systems are disruptive to clients, causing latency and data access disruptions due to the need to pause client I/O operations.
Innovation Solution
The use of a dirty region log and a metadata log to track and replicate client I/O operations, allowing for a non-disruptive transition to a synchronous replication state without holding client I/O operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current resynchronization processes are used to bring storage devices back into synchronous replication state, then data protection guarantees are restored, but client I/O operations are blocked causing latency and disruption
Solution Approach 1:
The patent segments the resynchronization process into distinct phases: identifying dirty regions that need synchronization, queueing client I/O operations separately, and processing synchronization in the background. This allows the system to maintain data protection through structured resynchronization while preventing client I/O blocking, thereby resolving the contradiction between reliability restoration and operational ease.
2Manufacturing precision
If client I/O operations are blocked during resynchronization, then data consistency between storage devices is ensured, but application performance deteriorates due to timeouts and errors
Solution Approach 1:
The patent implements preliminary action by pre-identifying dirty regions that require synchronization before client I/O operations proceed. By using a dirty region log to track which regions need synchronization and processing these in the background, the system ensures data consistency is maintained while allowing client applications to continue operating without timeouts or performance degradation.
3Reliability
If synchronous replication is implemented to provide greater data protection guarantees, then data loss protection is improved, but system complexity increases due to coordination requirements
Solution Approach 1:
The patent introduces intermediary mechanisms including a dirty region log and metadata log that act as mediators between the primary and secondary storage devices. These intermediaries track synchronization state and coordinate data transfer without requiring complex real-time coordination protocols, thereby maintaining strong data loss protection while reducing the operational complexity of synchronous replication.
Data Source
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AI summary
Techniques are provided for resynchronizing a synchronous replication relationship. Asynchronous incremental transfers are performed to replicate data of a storage object to a replicated storage object. Incoming write requests, targeting the storage object, are logged into a dirty region log during a last asynchronous incremental transfer. Metadata operations, executed on the storage object, are logged into a metadata log during the last asynchronous incremental transfer. Sequence numbers are assigned to the metadata operations based upon an order of execution. The metadata operations are replicated to the replicated storage object for execution according to the sequence numbers, and the dirty regions are replicated to the replicated storage object in response to the metadata operations having been replicated to the replicated storage object. The storage object and replicated storage object are transitioned to a synchronous replication state where incoming operations are synchronously replicated to the replicated storage object.