C Oracle Grid Infrastructure for a Cluster Installation Concepts

C.1.1.1 Understanding the Oracle Inventory Group

You must have a group whose members are given access to write to the Oracle Inventory (oraInventory) directory, which is the central inventory record of all Oracle software installations on a server. Members of this group have write privileges to the Oracle central inventory (oraInventory) directory, and are also granted permissions for various Oracle Clusterware resources, OCR keys, directories in the Oracle Clusterware home to which DBAs need write access, and other necessary privileges. By default, this group is called oinstall. The Oracle Inventory group must be the primary group for Oracle software installation owners.

The oraInventory directory contains the following:

• A registry of the Oracle home directories (Oracle Grid Infrastructure and Oracle Database) on the system

• Installation logs and trace files from installations of Oracle software. These files are also copied to the respective Oracle homes for future reference.

• Other metadata inventory information regarding Oracle installations are stored in the individual Oracle home inventory directories, and are separate from the central inventory.

You can configure one group to be the access control group for the Oracle Inventory, for database administrators (OSDBA), and for all other access control groups used by Oracle software for operating system authentication. However, this group then must be the primary group for all users granted administrative privileges.

C.1.1.2 Understanding the Oracle Inventory Directory

The Oracle Inventory directory (oraInventory) is the central inventory location for all Oracle software installed on a server.

The first time you install Oracle software on a system, you are prompted to provide an oraInventory directory path.

When you provide an Oracle base path when prompted during installation, or you have set the environment variable ORACLE_BASE for the user performing the Oracle Grid Infrastructure installation, OUI creates the Oracle Inventory directory in the path ORACLE_BASE/../oraInventory. For example, if ORACLE_BASE is set to /opt/oracle/11, then the Oracle Inventory directory is created in the path /opt/oracle/oraInventory, so that the central inventory for all installations is outside of the Oracle base for this particular Oracle installation user.

If you neither enter a path nor set ORACLE_BASE, then the Oracle Inventory directory is placed in the home directory of the user that is performing the installation. For example:

/home/oracle/oraInventory

As this placement can cause permission errors during subsequent installations with multiple Oracle software owners, Oracle recommends that you do not accept this option, and instead use an OFA-compliant path.

For new installations, Oracle recommends that you either create an Oracle path in compliance with OFA structure, such as /u01/app/oraInventory, that is owned by an Oracle software owner, or you set the Oracle base environment variable to an OFA-compliant value.

If you set an Oracle base variable to a path such as /u01/app/grid or /u01/app/oracle, then the Oracle Inventory is defaulted to the path u01/app/oraInventory using correct permissions to allow all Oracle installation owners to write to this central inventory directory.

By default, the Oracle Inventory directory is not installed under the Oracle base directory for the installation owner. This is because all Oracle software installations share a common Oracle Inventory, so there is only one Oracle Inventory for all users, whereas there is a separate Oracle base for each user.

C.1.2.1 Overview of the Oracle Base directory

During installation, you are prompted to specify an Oracle base location, which is owned by the user performing the installation. You can choose a location with an existing Oracle home, or choose another directory location that does not have the structure for an Oracle base directory.

Using the Oracle base directory path helps to facilitate the organization of Oracle installations, and helps to ensure that installations of multiple databases maintain an Optimal Flexible Architecture (OFA) configuration.

C.1.2.2 Understanding Oracle Base and Grid Infrastructure Directories

Even if you do not use the same software owner to install Grid Infrastructure (Oracle Clusterware and Oracle ASM) and Oracle Database, be aware that running the root.sh script during the Oracle Grid Infrastructure installation changes ownership of the home directory where clusterware binaries are placed to root, and all ancestor directories to the root level (/) are also changed to root. For this reason, the Oracle Grid Infrastructure for a cluster home cannot be in the same location as other Oracle software.

However, Oracle Grid Infrastructure for a standalone database--Oracle Restart--can be in the same location as other Oracle software.

C.1.3.1 About the Public IP Address

The public IP address is assigned dynamically using DHCP, or defined statically in a DNS or in a hosts file. It uses the public interface (the interface with access available to clients).

C.1.3.2 About the Private IP Address

Oracle Clusterware uses interfaces marked as private for internode communication. Each cluster node needs to have an interface that you identify during installation as a private interface. Private interfaces need to have addresses configured for the interface itself, but no additional configuration is required. Oracle Clusterware uses interfaces you identify as private for the cluster interconnect. If you identify multiple interfaces during information for the private network, then Oracle Clusterware configures them with Redundant Interconnect Usage. Any interface that you identify as private must be on a subnet that connects to every node of the cluster. Oracle Clusterware uses all the interfaces you identify for use as private interfaces.

For the private interconnects, because of Cache Fusion and other traffic between nodes, Oracle strongly recommends using a physically separate, private network. If you configure addresses using a DNS, then you should ensure that the private IP addresses are reachable only by the cluster nodes.

After installation, if you modify interconnects on Oracle RAC with the CLUSTER_INTERCONNECTS initialization parameter, then you must change it to a private IP address, on a subnet that is not used with a public IP address. Oracle does not support changing the interconnect to an interface using a subnet that you have designated as a public subnet.

You should not use a firewall on the network with the private network IP addresses, as this can block interconnect traffic.

C.1.3.3 About the Virtual IP Address

The virtual IP (VIP) address is registered in the GNS, or the DNS. Select an address for your VIP that meets the following requirements:

• The IP address and host name are currently unused (it can be registered in a DNS, but should not be accessible by a ping command)

• The VIP is on the same subnet as your public interface

C.1.3.4 About the Grid Naming Service (GNS) Virtual IP Address

The GNS virtual IP address is a static IP address configured in the DNS. The DNS delegates queries to the GNS virtual IP address, and the GNS daemon responds to incoming name resolution requests at that address.

Within the subdomain, the GNS uses multicast Domain Name Service (mDNS), included with Oracle Clusterware, to enable the cluster to map host names and IP addresses dynamically as nodes are added and removed from the cluster, without requiring additional host configuration in the DNS.

To enable GNS, you must have your network administrator provide a set of IP addresses for a subdomain assigned to the cluster (for example, grid.example.com), and delegate DNS requests for that subdomain to the GNS virtual IP address for the cluster, which GNS will serve. The set of IP addresses is provided to the cluster through DHCP, which must be available on the public network for the cluster.

C.1.3.5 About the SCAN

Oracle Database 11g release 2 clients connect to the database using SCANs. The SCAN and its associated IP addresses provide a stable name for clients to use for connections, independent of the nodes that make up the cluster. SCAN addresses, virtual IP addresses, and public IP addresses must all be on the same subnet.

The SCAN is a virtual IP name, similar to the names used for virtual IP addresses, such as node1-vip. However, unlike a virtual IP, the SCAN is associated with the entire cluster, rather than an individual node, and associated with multiple IP addresses, not just one address.

The SCAN works by being able to resolve to multiple IP addresses in the cluster handling public client connections. When a client submits a request, the SCAN listener listening on a SCAN IP address and the SCAN port is made available to a client. Because all services on the cluster are registered with the SCAN listener, the SCAN listener replies with the address of the local listener on the least-loaded node where the service is currently being offered. Finally, the client establishes connection to the service through the listener on the node where service is offered. All of these actions take place transparently to the client without any explicit configuration required in the client.

During installation listeners are created. They listen on the SCAN IP addresses provided on nodes for the SCAN IP addresses. Oracle Net Services routes application requests to the least loaded instance providing the service. Because the SCAN addresses resolve to the cluster, rather than to a node address in the cluster, nodes can be added to or removed from the cluster without affecting the SCAN address configuration.

The SCAN should be configured so that it is resolvable either by using Grid Naming Service (GNS) within the cluster, or by using Domain Name Service (DNS) resolution. For high availability and scalability, Oracle recommends that you configure the SCAN name so that it resolves to three IP addresses. At a minimum, the SCAN must resolve to at least one address.

If you specify a GNS domain, then the SCAN name defaults to clustername-scan.GNS_domain. Otherwise, it defaults to clustername-scan.current_domain. For example, if you start Oracle Grid Infrastructure installation from the server node1, the cluster name is mycluster, and the GNS domain is grid.example.com, then the SCAN Name is mycluster-scan.grid.example.com.

Clients configured to use IP addresses for Oracle Database releases prior to Oracle Database 11g release 2 can continue to use their existing connection addresses; using SCANs is not required. When you upgrade to Oracle Clusterware 11g release 2 (11.2), the SCAN becomes available, and you should use the SCAN for connections to Oracle Database 11g release 2 or later databases. When an earlier version of Oracle Database is upgraded, it registers with the SCAN listeners, and clients can start using the SCAN to connect to that database. The database registers with the SCAN listener through the remote listener parameter in the init.ora file. The REMOTE_LISTENER parameter must be set to SCAN:PORT. Do not set it to a TNSNAMES alias with a single address with the SCAN as HOST=SCAN.

The SCAN is optional for most deployments. However, clients using Oracle Database 11g release 2 and later policy-managed databases using server pools should access the database using the SCAN. This is because policy-managed databases can run on different servers at different times, so connecting to a particular node virtual IP address for a policy-managed database is not possible.