Adaptive Quorum Rules for Computer Cluster Recovery
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Solution Overview
Problem
Existing computer clusters face challenges in maintaining operation during unplanned disruptions, such as power outages or hardware failures, due to stringent quorum rules that can lead to total cluster outage even when some nodes remain operational.
Innovation Solution
Implementing adaptive recovery quorum rules that allow for flexible node configurations, enabling the cluster to continue operation with a subset of remaining nodes by ensuring they meet specific access requirements to voting file systems, either directly or indirectly through a coordinator node, and applying selection factors to determine the surviving subset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strict quorum rules are applied requiring majority of nodes to be online, then cluster consistency is maintained, but cluster availability deteriorates during disruptions
Solution Approach 1:
The patent implements dynamic quorum rules that adapt based on cluster state. During normal operation, strict quorum rules ensure consistency. During disruptions, the system dynamically transitions to more lenient rules that allow operation with fewer nodes, thus maintaining availability while preventing split-brain scenarios through coordinated state changes across all nodes.
Solution Approach 2:
The system changes the quorum parameter dynamically. Instead of a fixed majority requirement, the quorum threshold is adjusted based on the current cluster state and disruption type. This allows the cluster to operate with modified parameters during failures while maintaining safety guarantees through coordinated updates of these parameters across all nodes.
2Device complexity
If all nodes must have direct access to voting files, then quorum determination is simplified, but cluster resilience to storage failures deteriorates
Solution Approach 1:
The patent introduces an intermediary mechanism for voting file access. Instead of requiring every node to directly access voting files, the system uses intermediary nodes or proxies that can represent voting file access on behalf of other nodes. This maintains the logical quorum determination while providing resilience to storage failures through indirect access paths.
3Device complexity
If cluster size is fixed, then quorum calculation is straightforward, but adaptability to node failures deteriorates
Solution Approach 1:
The system transitions from static cluster size definitions to dynamic cluster size determination. The effective cluster size is continuously updated based on the current set of operational nodes, allowing the quorum calculation to adapt automatically to failures and recoveries without requiring complex manual reconfiguration or predetermined failure scenarios.
Data Source
AI summary
The fail-over computer cluster enables multiple computing devices to operate using adaptive quorum rules to dictate which nodes are in the fail-over cluster at any given time. The adaptive quorum rules provide requirements for communications between nodes and connections with voting file systems. The adaptive quorum rules include particular recovery rules for unplanned changes in node configuration, such as due to a disruptive event. Such recovery quorum rules enable the fail-over cluster to continuing to operate with various changed configurations of its node members as a result of the disruptive event. In the changed configuration, access to voting file systems may not be required for a majority-group subset of nodes. If no majority-group subset remains, nodes may need direct or indirect access to voting file systems.