Applies To:


Oracle Database : Oracle 12cR1 ( Enterprise Edition


Mahesh  Reddy



How do I change cluster mode from Standard Cluster to flex cluster?



After upgrade process from legacy oracle databases to oracle 12c, the cluster remains in standard cluster mode. It means flex cluster options are not enabled in this configuration. To get the full benefit, cluster mode has to be changed to flex cluster.

Please note that Cluster mode change  

  1. Involves cluster downtime
  2. Movement of standard cluster to flex cluster is supported, but not vice verse.
  3. Involves configuration of GNS with fixed IP, because flex cluster mode doesn't support static DNS IPs.

Cluster mode status change from standard cluster to flex cluster can be achieved with the below steps.

Step 1:  Run the following command to determine the current mode of the cluster:

# crsctl get cluster mode status

  cluster is running in “standard” mode

Step 2:  Run the following command to ensure that the Grid Naming Service (GNS) is configured with a fixed VIP:

$ srvctl config gns

This procedure cannot succeed unless GNS is configured with a fixed VIP. If there is no GNS, then as root create one as follows:

NOTE: before executing the following step, please ensure to make the GNS VIP IP entry in the DNS server.

$ srvctl add gns -vip vip_name | ip_address

Run the following command as root to start GNS:

$ srvctl start gns

Step 3:  Before changing the cluster mode, oracle flex ASM has to be enabled in cluster. Enable the flex ASM using ASMCA.

$ asmcmd showclustermode

  ASM cluster: Flex mode disabled

Step 4:  Now, using ASMCA you can convert oracle ASM configuration to oracle FLEX ASM. Before that we need to create password file in shared disk group using ORAPWD utility.

$ ORAPWD file=+OCR/asm.pwd password=***** entries=10

$ asmca

In ASM instances page you can select the “convert to oracle flex asm” dialogue box.

 In this tab, select the instances to perform the operations and then click the “convert to Oracle Flex ASM” dialogue box which is highlighted in RED. It will automatically open one more tab, which specifies the listener port and network interface for the conversion to flex ASM.

Select the network to be used for ASM network and then click OK button.

After that, run the above script as privileged user in local node for complete ASM conversion. This script should take some time for converting ASM configuration to flex ASM.

$ su – grid

Run the script “” as grid user.

Step 4: Now we can check the flex ASM mode

$ asmcmd showclustermode

 ASM Cluster: Flex mode enabled

Now, we can change the mode of the cluster to FLEX cluster as ‘ROOT’ user.


# crsctl set cluster mode flex

  Cluster mode set to “flex”

Changes to cluster mode will be effective after cluster service restart.

# crsctl stop crs

And then start the cluster in each node

# crsctl start crs

  Status of cluster mode is “FLEX”