Using Cluster File Systems

In Sun Cluster, all multihost disks are configured as disk device groups, which can be Solstice DiskSuite disksets, VxVM disk groups, or individual disks not under control of a software-based volume manager. Also, local disks are configured as disk device groups: a path leads to each local disk from each node. This setup does not mean the data on a disk is necessarily available from all nodes. The data only becomes available to all nodes if the file systems on the disks are mounted globally as a cluster file system.

A local file system that is made into a cluster file system only has a single connection to the disk storage. If the node with the physical connection to the disk storage fails, the other nodes no longer have access to the cluster file system. You can have local file systems on a single node that are not accessible directly from other nodes.

HA data services are set up so that the data for the service is stored on disk device groups in cluster file systems. This setup has several advantages. First, the data is highly available; that is, because the disks are multihosted, if the path from the node that currently is the primary fails, access is switched to another node that has direct access to the same disks. Second, because the data is on a cluster file system, it can be viewed from any cluster node directly--you do not have to log onto the node that currently masters the disk device group to view the data.