Multihost Devices

Disks that can be connected to more than one node at a time are multihost devices. In the Sun Cluster environment, multihost storage makes disks highly available. Sun Cluster software requires multihost storage for two-node clusters to establish quorum. Greater than two-node clusters do not require quorum devices. For more information about quorum, see Quorum and Quorum Devices.

Multihost devices have the following characteristics.

• Tolerance of single-node failures.

• Ability to store application data, application binaries, and configuration files.

• Protection against node failures. If clients request the data through one node and the node fails, the requests are switched over to use another node with a direct connection to the same disks.

• Global access through a primary node that “masters” the disks, or direct concurrent access through local paths. The only application that uses direct concurrent access currently is Oracle Real Application Clusters Guard.

A volume manager provides for mirrored or RAID-5 configurations for data redundancy of the multihost devices. Currently, Sun Cluster supports Solaris Volume Manager and VERITAS Volume Manager, which is available for use in only SPARC based clusters, as volume managers, and the RDAC RAID-5 hardware controller on several hardware RAID platforms.

Combining multihost devices with disk mirroring and disk striping protects against both node failure and individual disk failure.

See Chapter 4, Frequently Asked Questions for questions and answers about multihost storage.