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. Control the order in which nodes attempt to assume control if 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 more eligible secondary nodes can be promoted to primary. If service failover occurs, the nodelist that is set by the preferenced property 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 scconf(1M) command for VxVM disk device groups or the metaset(1M) command for Solaris Volume Manager device groups in conjunction with the preferenced and numsecondaries property settings to manage addition and removal of nodes from your configuration. Refer to “Administering Global Devices and Cluster File Systems” in Sun Cluster 3.1 System Administration GuideSun Cluster 3.1 System Administration Guide for procedural information about changing disk device group properties.