Applies to: 

Databases: Oracle 12cR1


Mahesh Reddy

Oracle 12c database has new features such as the oracle multitenant architecture, flex ASM, flex cluster, Information life cycle management enhancements just to name a few. Traditionally, IT organizations deploy databases and application on dedicated server infrastructures to support different types of workloads. Because of this dedicated deployments there is always a higher chance of

  • Underutilizing the resources.
  • Higher maintenance costs
  • Higher power consumption

 To addresses these challenges, oracle introduces oracle12c cloud database, which helps in consolidating multiple databases into single container database, which allows organizations to achieve greater efficiency in their operations by improving resource utilization and lowering both capital and operational expenditure. In order to consolidate multiple databases to cloud environment, there will be a need for powerful server infrastructure such as PowerEdge R920.

This wiki elaborates oracle 12c database new features with dell infrastructure.

  1. Oracle 12c database multitenant architecture
  2. Oracle 12c Flex cluster and Flex ASM
  3. Consolidation multiple 11gR2 databases into Oracle 12c container database as PDB’s
  4. Oracle 12c pluggable database plugging and unplugging

1. Multitenant Architecture:

These days, it is fairly common to find hundreds, or thousands, of databases scattered over almost as many machines, within customer sites of reasonable to large size. The associated expense has driven initiatives to bring lots of databases together, in other words to “consolidate” to reduce their costs.

Oracle multitenant is new option for Oracle database 12c, it helps the customers to reduce IT costs by simplifying consolidation, provisioning, upgrades and more.

The multitenant architecture enables an Oracle database to function as a multitenant container database (CDB).

Container Database (CDB): Every CDB has one root container (CDB$ROOT), one seed PDB (PDB$SEED) and zero or more user created PDB’s.

CDB$ROOT: it is exactly one root for each CDB which stores oracle supplied metadata (data dictionary) and common users.

PDB$SEED: it is system supplied template which is used to create new PDBs. We can’t add or modified objects in pdb$seed.

Pluggable Database (PDB): is a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a non-CDB.


Figure 1: oracle 12c Multi-tenant container data base (CDB)

This depicts the databases consolidation onto one server. Earlier days each database (BI,ERP, CRM, DW) has own memory, back ground process and database files on respective servers. So, each database using hardly 10% of hardware resources and 10% of administration time and also manage each database separately. This approach wastes both hardware and human resources. Oracle 12c database multitenant option enables to consolidate data and code without altering existing schemas or applications. Multitenant has many options to reduce cost for business improvement such as provisioning, easy cloning and consolidation. Hence, migrate legacy databases onto single container database which is on single server, share one database instance and one set of database files and background processes thereby minimizing hardware requirement.


  1. Cost reduction and easy administration
  2. Easy provisioning and performance tuning
  3. Manage many databases as one
  4. Easy patching and upgrades

2. Flex Cluster and Flex ASM:

In previous releases, Oracle clusters can accommodate between 32 to 64 nodes. But in this new release Oracle 12c, new feature Flex cluster is designed to scale up to 2000 nodes. Mainly, multitenant architecture of flex cluster can be used to efficiently extend the high availability frame work of oracle clusterware into the application tier. With flex cluster, we can manage multiple databases and applications running in a single cluster.

Flex cluster use hub and spoke topology.

This topology is the key architecture feature that segments the cluster into groups of nodes.

Two impacts of this topology:

A.   Limiting the size of hub to reduce the contention of OCR and Voting Disks

B.   Less heart beat network traffic.


Figure 2: Flex Cluster Architecture

Flex cluster:

This cluster provides tightly and loosely coupled servers into a single cluster. This configuration is scalable, dynamic and robust. In oracle Flex Cluster, the nodes are arranged in two ways i.e. Hub Node and Leaf Node. The Hub Nodes are tightly connected with each other like standard configuration and have direct access to the shared storage. A maximum 64 hub nodes can be configured in a cluster. The number of Leaf Nodes can be many more. Hub Nodes and Leaf Nodes can host different types of applications.

Hub Node:

Hub Nodes are similar to Oracle Grid Infrastructure nodes in an Oracle Clusterware standard Cluster configuration. They are tightly connected and have direct accesses to shared storage.

Leaf Node:

Leaf Nodes are different from standard Oracle Grid Infrastructure nodes, and they do not require direct access to shared storage, but instead request data through Hub Nodes. Leaf Nodes must be members of a cluster that includes at least one Hub Node.

Managing Flex clusters:

To install an Oracle 12c flex cluster, visit wiki


Get the cluster mode status

$ crsctl get cluster mode status

  Cluster is running in “flex” mode

If the cluster is running in standard mode, we can easily change from standard to flex mode using CRSCTL utility. Refer this wiki.

Flex ASM:

Pre Oracle 12c, each node has database instance and ASM instance. But in Oracle 12c, database instance and ASM instance can be on different servers. In Flex mode where cluster has more than 3 nodes would only run 3 ASM instances much like how SCAN works. Unlike SCAN, a two node cluster would have 2 ASM instances, not 3.

Manage ASM instance:

Oracle Flex ASM enables Oracle ASM instances to run on a separate physical server from the database servers. When using Oracle Flex ASM, you can configure Oracle ASM clients with direct access to storage or the I/O can be sent through a pool of I/O servers. Every cluster has at least one private network and one public network. If the cluster is going to use Oracle ASM for storage, it has at least one Oracle ASM network. A single network can be used as both a private and an Oracle ASM network. For security reasons, an Oracle ASM network should never be public.

ASM Network:

With oracle Flex ASM 12c, a new type of network called “ASM network” is introduced. It is used for communication between ASM and its clients and is accessible on all the nodes. It is possible to configure single network that can perform both functions of private and ASM networks.

How to setup oracle flex ASM:

During the Oracle 12c installation process, we can choose the type of the oracle Clusterware that should be installed. Refer wiki

You can use the ASMCMD command to determine whether Oracle Flex ASM is enabled.

$ asmcmd showclustermode

  ASM cluster: Flex mode enabled

Use SRVCTL to determine the status of the instances in an Oracle Flex ASM configuration.

$ srvctl status asm -detail

  ASM is running on db12c1, db12c3, db12c2

  ASM is enabled.

Converting to oracle Flex ASM:

This functionality is only available in oracle 12c grid configuration. You can convert an Oracle ASM configuration to an Oracle Flex ASM using ASMCA. Please refer wiki.

3. Consolidation of Databases:

Oracle 12c database offers significant advantages of consolidating application workloads.

They are:

  1. Easy consolidation using Dell storage snapshot with minimal down time
  2. Reduce the different environment databases manage many as ONE.
  3. Easy patching and cloning.
  4. Consolidation lowers cost and improves business functionality.

Below diagram depicts multiple databases consolidated into single container database. For guidance to migrate or consolidate legacy databases, refer white paper.

Figure 3: consolidating multiple databases into single container

4. Oracle 12c Pluggable Database:

In oracle 12c, each CDB has one seed PDB and created one or more pluggable databases. Each CDB has 0 to 252 databases on a single server. Please refer this wiki on how to create PDB and how to unplug and plug it back to the same CDB or remote CDB and how to create PDB using clone PDB and SEED PDB.

                        Figure 4: Plug in an unplugged PDB