What is Oracle Flex Cluster

Oracle Flex Cluster Explained

What is Oracle Flex Cluster

Oracle 12c Flex Clusters use hub-and-spoke technology, allowing the cluster to scale much beyond the pre-12c clusters as it requires.

Maximum 64 hub nodes
can be as many as leaf nodes
Hub nodes are connected to storage.
Leaf nodes do not require to be directly connected to storage They access the data through hub nodes
Flex cluter may operate with one or many hub nodes but leaf nodes are optional and can only exists as member of cluster that includes atleat one hub node

What is hub Node in Flex Cluster

A hube node is same as pre 12 cluster node. Each hub node are tightly connected to each other via private interconnect and form the cluster
A hub node hosts database and ASM instances
Each hub node access the shared storage

What is Leaf Node in Flex Cluster

leaf nodes are loosely connected with the cluster.
Each leaf node is connected to the hub node and therefore connected to cluster via hub node only
leaf nodes are not connected to each other
They can not host database and ASM instances
All Leaf Nodes are on the same public and private network as the Hub Nodes
Leaf Nodes can failover to a different node if the Leaf Node fails.
Leaf Nodes can host different types of applications e.g. Fusion Middleware, EBS, IDM, etc. The applications on

What happens with the Leaf nodes connected to a Hub Node if the Hub Node is no more in Cluster
 Leaf Nodes associated with that Hub Node failover to one of the surviving nodes in the cluster.

How to identify a Leaf and Hub Node

$ crsctl get node role status -all
Node 'node1' active role is 'hub'
Node 'node2' active role is 'hub'

Benefits of using a cluster

Scalability of applications (including Oracle RAC and Oracle RAC One databases)
.Overview of Oracle Clusterware
• Reduce total cost of ownership for the infrastructure by providing a scalable system with low-cost commodity hardware
• Ability to fail over
• Increase throughput on demand for cluster-aware applications, by adding servers to a cluster to increase cluster resources
• Increase throughput for cluster-aware applications by enabling the applications to run on all of the nodes in a cluster
• Ability to program the startup of applications in a planned order that ensures dependent processes are started in the correct sequence
• Ability to monitor processes and restart them if they stop
• Eliminate unplanned downtime due to hardware or software malfunctions
• Reduce or eliminate planned downtime for software maintenance

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