Mediator Reseeding for Cross-Site Storage Consistency
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Solution Overview
Problem
Cross-site storage solutions face resilience issues due to mediator unavailability, leading to connectivity problems and potential data consistency issues during failover operations, as the mediator cannot be trusted to act as an arbitrator when its relationship state information is inconsistent or stale.
Innovation Solution
Implement a mediator reseed process that updates stale consistency group relationship information when the mediator becomes available, using a reseed status indicator to prevent simultaneous reseed processes and ensure correct failover operations by serializing mediator reseed operations and tracking changes in data replication status.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the mediator is allowed to act as an arbitrator during unavailability, then failover operations can continue, but data consistency issues arise due to stale relationship state information
Solution Approach 1:
The system performs preliminary actions by detecting mediator unavailability and preventing the mediator from acting as an arbitrator before data consistency issues can occur. The change detector continuously monitors for changes in data replication status during mediator unavailability, and the reseed process updates the mediator's relationship state information before it can make incorrect arbitration decisions.
2Reliability
If the mediator's relationship state information is updated continuously, then data consistency is maintained, but system complexity increases
Solution Approach 1:
The system implements self-service by having the change detector automatically monitor data replication status changes and trigger reseed operations when needed. The mediator reseed process automatically updates the mediator's relationship state information without requiring manual intervention, and the reseed status indicator automatically prevents simultaneous reseed processes, making the system self-managing and reducing operational complexity.
3Speed
If simultaneous mediator reseed processes are allowed, then processing speed increases, but data consistency issues occur due to conflicting updates
Solution Approach 1:
The system applies preliminary anti-action by using the reseed status indicator to prevent simultaneous mediator reseed processes before conflicting updates can occur. The indicator is set to a second state when a reseed process is initiated, and this state is checked before starting another reseed process, thereby preemptively blocking potential conflicts and ensuring data consistency.
Data Source
AI summary
Systems and methods for making a cross-site storage solution resilient towards mediator unavailability are provided. According to one embodiment, a stretched storage system is operable to bring a mediator associated with a primary and secondary distributed storage system back into the role of an arbitrator for peered consistency groups (CGs). A mediator reseed status indicator is maintained for multiple CGs to identify when the mediator's status information for a CG is stale. When the mediator becomes available and a local CG is identified as the subject of a mediator reseed process, the master node of the primary that hosts a master copy of a dataset for the local CG performs the reseed process, including: (i) causing relationship status information for the local CG to be updated on the mediator to the current state maintained by the primary; and (ii) resetting the mediator reseed status indicator.