You cannot create fault groups for an Eon Mode database. Rather, Vertica automatically creates fault groups on a large cluster Eon database; these fault groups are configured around the control nodes and their dependents of each subcluster. These fault groups are managed internally by Vertica and are not accessible to users.
Fault groups let you configure an Enterprise Mode database for your physical cluster layout. Sharing your cluster topology lets you use terrace routing to reduce the buffer requirements of large queries. It also helps to minimize the risk of correlated failures inherent in your environment, usually caused by shared resources.
Vertica automatically creates fault groups around control nodes (servers that run spread) in large cluster arrangements, placing nodes that share a control node in the same fault group. Automatic and user-defined fault groups do not include ephemeral nodes because such nodes hold no data.
Consider defining your own fault groups specific to your cluster's physical layout if you want to:
- Use terrace routing to reduce the buffer requirements of large queries.
- Reduce the risk of correlated failures. For example, by defining your rack layout, Vertica can better tolerate a rack failure.
- Influence the placement of control nodes in the cluster.
Vertica supports complex, hierarchical fault groups of different shapes and sizes. The database platform provides a fault group script (DDL generator), SQL statements, system tables, and other monitoring tools.
See High Availability with Fault Groups for an overview of fault groups with a cluster topology example.