Disk Device Groups

In Sun Cluster, all multihost disks must be under control of the Sun Cluster framework. You first create volume manager disk groups--either Solstice DiskSuite disksets or VERITAS Volume Manager disk groups--on the multihost disks. Then, you register the volume manager disk groups as Sun Cluster disk device groups. A disk device group is a type of global device. In addition, Sun Cluster registers every individual disk as a disk device group.

Disk device groups are independent of resource groups. One node can master a resource group (representing a group of data service processes) while another can master the disk group(s) being accessed by the data services. However, the best practice is to keep the disk device group that stores a particular application's data and the resource group that contains the application's resources (the application daemon) on the same node. Refer to the overview chapter in the Sun Cluster 3.0 Data Services Installation and Configuration Guide for more information about the association between disk device groups and resource groups.

With a disk device group, the volume manager disk group becomes "global" because it provides multipath support to the underlying disks. Each cluster node physically attached to the multihost disks provides a path to the disk device group.

A global device is highly available if it is part of a device group that is hosted by more than one cluster node.

Disk Device Failover

Because a disk enclosure is connected to more than one node, all disk device groups in that enclosure are accessible through an alternate path if the node currently mastering the device group fails. The failure of the node mastering the device group does not affect access to the device group except for the time it takes to perform the recovery and consistency checks. During this time, all requests are blocked (transparently to the application) until the system makes the device group available.

Figure 3-2 Disk Device Group Failover