This section describes disk device group properties that enable you to balance performance and availability in a multiported disk configuration. Sun Cluster software provides two properties used to 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 a desired number of secondary nodes for a device group.
A highly available service is considered down when the primary goes down and when no eligible secondary nodes can be promoted to primary. If service failover occurs and the preferenced property is true, then the nodes follow the order in the nodelist to select a secondary. the nodelist that is set by the defines the order in which nodes will attempt to assume primary control or transition from spare to secondary. You can dynamically change the preference of a device service by using the scsetup(1M) utility. The preference that is associated with dependent service providers, for example a global file system, will be that 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 caused by checkpointing. By default, your disk device group will have one primary and one secondary. The remaining available provider nodes will come online in the spare state. If failover occurs, the secondary will become primary and the node highest in priority on the nodelist will become secondary.
The desired number of secondary nodes can be set to any integer between one and the number of operational non-primary provider nodes in the device group.
If you are using Solaris Volume Manager, you must create the disk device group before you can set the numsecondaries property to a number other than the default.
The default desired number of secondaries for device services is one. The actual number of secondary providers that is maintained by the replica framework is the desired number, unless the number of operational non-primary providers is less than the desired number. You will want to alter the numsecondaries property and double check the nodelist if you are adding or removing nodes from your configuration. Maintaining the nodelist and desired number of secondaries will prevent conflict between the configured number of secondaries and the actual number allowed by the framework.Use the metaset(1M) command for Solaris Volume Manager device groups or, if you're using Veritas Volume Manager, the scconf(1M) command for VxVM disk device groups in conjunction with the preferenced and numsecondaries property settings to manage addition and removal of nodes from your configuration. Refer to “Administering Cluster File Systems Overview” in Sun Cluster System Administration Guide for Solaris OS for procedural information about changing disk device group properties.