1.2.6 Multihost Disks

In all Sun Cluster configurations, two or more nodes are physically connected to a set of shared, or multihost, disks. The shared disks are grouped across disk expansion units. Disk expansion units are the physical disk enclosures. Sun Cluster supports various disk expansion units: Sun StorEdge^TM MultiPack, Sun StorEdge A3000, and Sun StorEdge A5000 units, for example. Figure 1-7 shows two hosts, both physically connected to a set of disk expansion units. It is not required that all cluster nodes are physically connected to all disk expansion units.

In HA configurations, the multihost disks contain the data for highly available data services. A server can access data on a multihost disk when it is the current master of that disk. In the event of failure of one of the Sun Cluster servers, the data services fail over to another server in the cluster. At failover, the data services that were running on the failed node are started on another node without user intervention and with only minor service interruption. The system administrator can switch over data services manually at any time from one Sun Cluster server to another. Refer to "1.5.10 System Failover and Switchover", for more details on failover and switchover.

In parallel database configurations, the multihost disks contain the data used by the relational database application. Multiple servers access the multihost disk simultaneously. User processes are prevented from corrupting shared data by the Oracle UNIX Dynamic Lock Manager (DLM). If one server connected to a multihost disk fails, the cluster software recognizes the failure and routes user queries through one of the remaining servers.

All multihost disks with the exception of the Sun StorEdge A3000 (with RAID5) must be mirrored. Figure 1-7 shows a multihost disk configuration.

Figure 1-7 Local and Multihost Disks