2.1.1 Shared Volume Manager Objects

When used with CVM, volume manager objects are capable of being shared by all of the nodes in a given cluster.

CVM allows for two types of disk groups:

• Private disk groups, which belong to only one node. A private disk group is only imported by one system. Disks in a private disk group can be physically accessible from one or more systems, but actual access is restricted to one system only.

• Cluster-shareable disk groups, which are shared by all nodes. A cluster-shareable (or shared) disk group is imported by all cluster nodes. Disks in a cluster-shareable disk group must be physically accessible from all systems that can join the cluster.

With CVM, most disk groups are shared. However, the root disk group (rootdg) is always a private disk group.

The volume manager disks within a shared disk group are shared by all of the nodes in a cluster, so multiple nodes in a cluster can access a given volume manager disk simultaneously. Likewise, all volumes in a shared disk group can be shared by all nodes in a cluster. A volume manager disk or volume is considered shared when it is accessed by more than one node at the same time.

Only raw device access is performed through CVM. CVM does not support shared volumes with file systems. CVM does not currently support RAID5 volumes in cluster-shareable disk groups. RAID5 volumes can, however, be used in private disk groups attached to specific nodes of a cluster.