Data Replication Recovery Using Out-of-Sync Bitmaps
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Solution Overview
Problem
In data replication environments, the process of mirroring updates from a secondary storage device back to a primary storage device after an outage is time-consuming, leading to prolonged downtime and increased bandwidth requirements during the resynchronization process.
Innovation Solution
The method involves using out-of-sync bitmaps to track updated data elements and redirect I/O operations from the secondary site to the primary site when the expected I/O latency difference reaches a threshold, allowing for accelerated recovery and reduced bandwidth usage by ensuring that only necessary data is copied back to the primary site.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If updated data elements are copied from secondary site to primary site after failover, then data consistency is maintained, but recovery time increases significantly
Solution Approach 1:
The system performs preliminary actions by maintaining out-of-sync bitmaps during the outage period that track which data elements have been updated at the secondary site. When failback is initiated, these pre-computed bitmaps allow the system to immediately identify and copy only the necessary updated data elements without needing to analyze or scan all data, thereby dramatically reducing recovery time while maintaining data consistency.
2Reliability
If all updated data is mirrored back to primary site, then complete data consistency is achieved, but bandwidth consumption increases
Solution Approach 1:
The system extracts only the necessary information (out-of-sync data elements) from the complete data set by using bitmaps that track which specific data elements have been updated at the secondary site. During failback, only these extracted updated elements are copied to the primary site, rather than copying all data, thereby significantly reducing bandwidth consumption while achieving complete data consistency for the updated elements.
3Productivity
If I/O is redirected to secondary site during recovery, then production continuity is maintained, but I/O latency increases
Solution Approach 1:
The system dynamically switches I/O routing based on the recovery state. During the initial recovery phase when data synchronization is ongoing, I/O is redirected to the secondary site to maintain production continuity. As the recovery process progresses and data consistency is achieved (detected through bitmap comparison), the system dynamically redirects I/O back to the primary site, thereby optimizing the balance between production continuity and I/O latency at different stages of recovery.
Data Source
AI summary
A method for optimizing recovery in a data replication environment is disclosed. In one embodiment, such a method includes directing I/O from a primary site to a secondary site in response to a failure at the primary site. After the primary site has recovered from the failure, the method initiates a recovery process wherein updated data elements at the secondary site are copied to the primary site. The method determines a recorded average I/O latency for a host system driving I/O to the secondary site, and calculates an expected average I/O latency for the host system driving I/O to the primary site. The method redirects I/O from the secondary site to the primary site when a difference between the expected average I/O latency and the recorded average I/O latency reaches a threshold value. A corresponding system and computer program product are also disclosed.