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| Oracle Solaris Cluster Data Services Planning and Administration Guide Oracle Solaris Cluster 4.1

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## Relationship Between Resource Groups and Device Groups

Oracle Solaris Cluster uses the concept of node lists for 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. Oracle Solaris Cluster uses a failback policy to determine the behavior of Oracle Solaris Cluster in response to the following set of conditions:

- A node that has failed and left the cluster rejoins the cluster.

- The node that is rejoining the cluster appears earlier in the node list than the current primary node.

If failback is set to `True`, the device group or resource group is switched off the current primary and switched onto the rejoining node, making the rejoining node the new primary.

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. This setting 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.

For more information about the relationship between device groups and resource groups, see Device Groups in Oracle Solaris Cluster Concepts Guide.

For information about how to set up device groups, see the following documentation:

- Planning Device Groups in Oracle Solaris Cluster Software Installation Guide

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