HP Serviceguard Extension for RAC (SGeRAC) manual How Cluster Interconnect Subnet Works

Oracle 10g/11gR1/11gR2 RAC uses the following two subnets for cluster communication purposes:

•CSS Heartbeat Network (CSS-HB)—Oracle Clusterware running on the various nodes of the cluster communicate among themselves using this network.

•RAC Cluster Interconnect Network (RAC-IC)—Database instances of a database use this network to communicate among themselves.

NOTE: In this document, the generic terms CRS and Oracle Clusterware will subsequently be referred to as Oracle Cluster Software. The use of the term CRS will still be used when referring to a sub-component of Oracle Cluster Software.

For more detailed information on Oracle 10g/11gR1/11gR2 RAC, refer to Chapter 2: “Serviceguard Configuration for Oracle 10g, 11gR1, or 11gR2 RAC”.

Overview of SGeRAC Cluster Interconnect Subnet Monitoring

In SGeRAC, the Cluster Interconnect Subnet Monitoring feature is used to monitor cluster communication subnets. This feature requires the use of a package configuration parameter known as the CLUSTER_INTERCONNECT_SUBNET. It can be set up to monitor certain subnets used by applications that are configured as Serviceguard multi-node packages.

The following describes the characteristics of subnets that can be monitored by using the CLUSTER_INTERCONNECT_SUBNET parameter:

•A subnet used only for the communications among instances of an application configured as a multi-node package.

•A subnet whose health does not matter if there is only one instance of an application (package) running in the cluster. The instance is able to provide services to its clients regardless of whether the subnet is “up” or “down” on the node where the only instance of the package is running.

A failure of the cluster interconnect subnet on all nodes of the cluster, where the multi-node package is running, is handled by bringing down all but one instance of the multi-node package.

In certain 10g/11gR1/11gR2 RAC configurations, this parameter can be used to monitor Oracle Cluster Synchronization Services (CSS-HB) and/or RAC cluster interconnect subnet when Oracle Clusterware and RAC Database instances are configured as Serviceguard multi-node packages.

Cluster Interconnect Subnet Monitoring provides the following benefits:

•Better availability by detecting and resolving RAC-IC subnet failures quickly in certain configurations. (For example, in configurations where Oracle CSS-HB subnet and the RAC-IC subnet are not the same. This configuration helps avoid one RAC database (RAC-IC) traffic from interfering with another.)

•Assists in providing services (on one node) when Oracle CSS-HB/RAC-IC subnet fails on all nodes.

•Facilitates fast and reliable reconfiguration with use of multiple SG-HB networks.

•Allows separation of SG-HB and Oracle RAC-IC traffic (recommended when RAC-IC traffic may interfere with SG-HB traffic).

How Cluster Interconnect Subnet Works

The CLUSTER_INTERCONNECT_SUBNET parameter works similar to the existing SUBNET package configuration parameter. The most notable difference is in the failure handling of the subnets monitored using these individual parameters.

While the failure of subnets monitored using SUBNET package configuration parameter is handled by halting the instance of the package on the node where the subnet has failed, the failure of subnets monitored using CLUSTER_INTERCONNECT_SUBNET package configuration parameter is handled by ensuring at least one instance of the multi-node package remains running in the cluster.

Overview of SGeRAC Cluster Interconnect Subnet Monitoring 17