Cross-Subnet Configurations in Extended Distance Clusters

As of Serviceguard A.11.18 it is possible to configure multiple subnets, joined by a router, both for the cluster heartbeat and for data, with some nodes using one subnet and some another.

A cross-subnet configuration allows:

Automatic package failover from a node on one subnet to a node on another
A cluster heartbeat that spans subnets.




	NOTE: For detailed information on configuring cross-subnet see the Managing Serviceguard Sixteenth Edition user’s guide.

Restrictions

Beginning with the Serviceguard A.11.18 patches, PHSS_37094 (11i v2) and PHSS_37095 (11i v3), Cross-Subnet configurations are supported. This allows the nodes in each data center to configure their heartbeats on subnets that are locally unique to their own data centers.

The following restrictions apply when configuring Cross-Subnet:

All nodes in the cluster must belong to the same network domain (that is, the domain portion of the fully-qualified domain name must be the same).
The nodes must be fully connected at the IP level.
A minimum of two heartbeat paths must be configured for each cluster node.
There must be less than 200 milliseconds of latency in the heartbeat network.
Each heartbeat subnet on each node must be physically routed separately to the heartbeat subnet on another node; that is, each heartbeat path must be physically separate:
- The heartbeats must be statically routed; static route entries must be configured on each node to route the heartbeats through different paths.
- Failure of a single router must not affect both heartbeats at the same time.
Because CVM and CFS require link-level traffic communication (LLT) among the nodes, Extended Clusters cannot be configured in Cross-Subnet configurations with CVM or CFS. As a result, only Extended Clusters using LVM volume groups are supported in Cross-Subnet configurations.
Because Oracle RAC requires a common subnet for the RAC interconnect between nodes, Extended RAC Cross-Subnet Clusters are not supported.

Each package subnet must be configured with a standby interface on the local bridged net. The standby interface can be shared between subnets.




	NOTE: Deploying applications in this environment requires careful consideration; see “Implications for Application Deployment” on page 188 in the Managing Serviceguard Sixteenth Edition user’s guide.

cmrunnode will fail if the “hostname LAN” is down on the node in question. (“Hostname LAN” refers to the public LAN on which the IP address that the node’s hostname resolves to is configured).
If a monitored_subnet is configured for PARTIAL monitored_subnet_access in a package’s configuration file, it must be configured on at least one of the nodes on the node_name list for that package. Conversely, if all of the subnets that are being monitored for this package are configured for PARTIAL access, each node on the node_name list must have at least one of these subnets configured.
- A package will not start on a node unless the monitored subnets configured on that node, and specified in the package configuration file as monitored subnets, are up.

Cross-Subnet Configuration with Two Data Centers

Figure 2-1 is an example of a two data center configuration using WDM for both storage and networking.

Figure 2-1 Two Data Centers with Cross-Subnet




	IMPORTANT: Although this topology can be implemented on a single site, it is most commonly used by extended-distance clusters, and Metrocluster, which require HP add-on software. Design and configuration of such clusters are covered in the disaster-tolerant documentation delivered with Serviceguard. For more information, see the following documents at `http://docs.hp.com`-> High Availability: Understanding and Designing Serviceguard Disaster Tolerant Architectures Designing Disaster Tolerant HA Clusters Using Metrocluster and Continentalclusters Using Serviceguard Extension for RAC user's guide The white paper Configuration and Administration of Oracle 10g RAC Database in HP Metrocluster

Cross-Subnet Configurations in Extended Distance Clusters

Technical documentation

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Restrictions

Cross-Subnet Configuration with Two Data Centers

Further Reading