Relationship Between Resource Groups and Disk Device Groups

Sun Cluster uses the concept of node lists for disk device groups and resource groups. Node lists are ordered lists of primary nodes, which are potential masters of the disk device group or resource group. Sun Cluster uses a failback policy to determine what happens when a node has been down and then rejoins the cluster, and the rejoining node appears earlier in the node list than the current primary node. If failback is set to True, the device group or resource group will be switched off of the current primary and switched onto the rejoining node, making the rejoining node the new primary.

To ensure high availability of a failover resource group, make the resource group's node list match the node list of associated disk device groups. For a scalable resource group, the resource group's node list cannot always match the device group's node list because, currently, a device group's node list must contain exactly two nodes. For a greater-than-two-node cluster, the node list for the scalable resource group can have more than two nodes.

For example, assume that you have a disk device group, disk-group-1, that has nodes phys-schost-1 and phys-schost-2 in its node list, with the failback policy set to Enabled. Assume that you also have a failover resource group, resource-group-1, which uses disk-group-1 to hold its application data. When you set up resource-group-1, also specify phys-schost-1 and phys-schost-2 for the resource group's node list, and set the failback policy to True.

To ensure high availability of a scalable resource group, make the scalable resource group's node list a superset of the node list for the disk device group. Doing so ensures that the nodes that are directly connected to the disks are also nodes that can run the scalable resource group. The advantage is that, when at least one cluster node connected to the data is up, the scalable resource group runs on that same node, making the scalable services available also.

See the Sun Cluster 3.1 Software Installation Guide for information on how to set up disk device groups. See the Sun Cluster 3.1 Concepts Guide document for more details on the relationship between disk device groups and resource groups.