This section describes device group properties that enable you to balance performance and availability in a multiported disk configuration. Sun Cluster software provides two properties that configure a multiported disk configuration: preferenced and numsecondaries. You can control the order in which nodes attempt to assume control if a failover occurs by using the preferenced property. Use the numsecondaries property to set the number of secondary nodes for a device group that you want.
A highly available service is considered down when the primary node fails and when no eligible secondary nodes can be promoted to primary nodes. If service failover occurs and the preferenced property is true, then the nodes follow the order in the node list to select a secondary node. The node list defines the order in which nodes attempt to assume primary control or transition from spare to secondary. You can dynamically change the preference of a device service by using the clsetup command. The preference that is associated with dependent service providers, for example a global file system, is identical to the preference of the device service.
Secondary nodes are check-pointed by the primary node during normal operation. In a multiported disk configuration, checkpointing each secondary node causes cluster performance degradation and memory overhead. Spare node support was implemented to minimize the performance degradation and memory overhead that checkpointing caused. By default, your device group has one primary and one secondary. The remaining available provider nodes become spares. If failover occurs, the secondary becomes primary and the node or highest in priority on the node list becomes secondary.
You can set the number of secondary nodes that you want to any integer between one and the number of operational nonprimary provider nodes in the device group.
If you are using Solaris Volume Manager, you must create the device group before you can set the numsecondaries property to a number other than the default.
The default number of secondaries for device services is 1. The actual number of secondary providers that is maintained by the replica framework is the number that you want, unless the number of operational nonprimary providers is less than the number that you want. You must alter the numsecondaries property and double-check the node list if you are adding or removing nodes from your configuration. Maintaining the node list and number of secondaries prevents conflict between the configured number of secondaries and the actual number that is allowed by the framework.
(Solaris Volume Manager) Use the metaset command for Solaris Volume Manager device groups, in conjunction with the preferenced and numsecondaries property settings, to manage the addition of nodes to and the removal of nodes from your configuration.
(Veritas Volume Manager) Use the cldevicegroup command for VxVM device groups, in conjunction with the preferenced and numsecondaries property settings, to manage the addition of nodes to and the removal of nodes from your configuration.
Refer to Overview of Administering Cluster File Systems in Sun Cluster System Administration Guide for Solaris OS for procedural information about changing device group properties.