Tag Archives: Hub nodes

What is Oracle Flex Cluster?

What is Oracle Flex Cluster?

Oracle Grid Infrastructure installed in an Oracle Flex Cluster configuration is a scalable, dynamic, robust network of nodes.
CRSCTL to manage Oracle Flex Clusters after successful installation of Oracle Grid Infrastructure.

Oracle Flex Clusters contain two types of nodes : Hub & leaf nodes

Hub nodes is same as default cluster node and having direct access to shared storage. It used for both read or write operation.
Leaf nodes is not directly connected with shared storage, it connected through hub nodes. It used for read operation.

Following are the few important points regarding hub nodes and leaf node. which will help us to understand the flex cluster:

  • The number of Hub Nodes in an Oracle Flex Cluster can be as many as 64.
  • The number of Leaf Nodes can be many more.
  • Hub Nodes and Leaf Nodes can host different types of applications.
  • Hub Nodes are similar to Oracle Grid Infrastructure nodes in an Oracle Clusterware they are tightly integrade and have shared storage.
  • Use Hub Nodes to host read-write database instances.
  • Leaf Nodes are different they donot have direct access to shared storage, request data from hub node.
  • Use Leaf Nodes to host read-only database instances.


  • Leaf Nodes must be members of a cluster that includes at least one Hub Node.
  • During planned shutdown of Hub Nodes, a Leaf Node attempts to connect to another Hub Node, unless it connected to only one hub node.
  • Hub Node is evicted, then the Leaf Node is also evicted.