Using Serviceguard Extension for RAC, 8th Edition, March 2009

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 detail information on Oracle 10g/11gR1 RAC refer to Chapter 2: “Serviceguard
Configuration for Oracle 10g or 11gR1 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_SUBNETparameter:
• 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 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.
For example, when a multi-node package (pkgA) is configured to run on all nodes of the cluster,
and configured to monitor a subnet (SubnetA) using the CLUSTER_INTERCONNECT_SUBNET
parameter:
Overview of SGeRAC Cluster Interconnect Subnet Monitoring 19