What are voting disks and their uses?
In Oracle Real Application Clusters (RAC), the Voting Disk is a critical component that plays a crucial role in maintaining cluster integrity and preventing split-brain scenarios. The Voting Disk is used to determine the membership and health of nodes in the cluster. It is an essential part of the Oracle Clusterware infrastructure.
Purpose:
The primary purpose of the Voting Disk is to prevent split-brain scenarios in a clustered environment. A split-brain occurs when nodes in a cluster lose communication with each other but continue to operate independently. The Voting Disk helps in identifying the surviving partition of the cluster.
Important Key points about the Voting Disk:
Membership and Quorum:
Each node in the Oracle RAC cluster participates in a voting mechanism. The Voting Disk keeps track of the votes from each node, and a majority of votes is required to establish cluster membership and maintain quorum. Quorum is crucial for making consistent decisions about the state of the cluster.
Redundancy:
For increased reliability and fault tolerance, Oracle RAC often maintains multiple copies of the Voting Disk. This copies is maintained in odd number of terms like 1, 3, 5 etc. The redundancy helps in avoiding a single point of failure. Multiple copies allow the cluster to continue functioning even if some copies become inaccessible.
Location for Storage:
The Voting Disk is typically stored on shared storage that is accessible to all nodes in the cluster. It can be a raw disk partition, a cluster file system, or other shared storage solutions.
Dynamic Adjustment:
The Oracle Clusterware dynamically adjusts the number of votes assigned to each node based on the cluster configuration. Nodes may have multiple votes, and the total number of votes determines the cluster quorum.
Maintenance and Management:
Oracle provides tools and utilities, such as the crsctl command-line utility, to manage and configure the Voting Disk. Administrators can add or remove Voting Disk locations, check the integrity of the cluster, and perform other maintenance tasks.
Failure Scenarios:
If a node loses communication with the rest of the cluster or if it becomes unavailable, the Voting Disk helps in determining whether the node is truly down or if there is a network partition. In case of a network partition, the Voting Disk helps in deciding which nodes should remain in the cluster.
