HP UX Serviceguard Storage Management Software manual Private and Shared Disk Groups

Figure 4-1

Cluster Volume Manager Administration

Overview of Cluster Volume Management

Example of a 4-Node Cluster

Redundant Private Network

Node 0

Master

Node 1

Slave

Node 2

Slave

Node 3

Slave

NOTE

Redundant

Fibre Channel

Connectivity

Cluster-Shareable

Disks

Cluster-Shareable

Disk Groups

To the cmvx daemon, all nodes are the same. VxVM objects configured within shared disk groups can potentially be accessed by all nodes that join the cluster. However, the cluster functionality of VxVM requires that one node act as the master node; all other nodes in the cluster are secondary nodes. Any node is capable of being a master node. The master node is responsible for coordinating certain VxVM activities.

You must run commands that configure or reconfigure VxVM objects on the master node. Tasks that must be initiated from the master node include setting up shared disk groups, creating and reconfiguring volumes, and performing snapshot operations.

VxVM designates the first node to join a cluster as the master node for that cluster. If the master node leaves the cluster, one of the secondary nodes is chosen to be the new master node. In Figure 4-1, Example of a 4-Node Cluster, node 0 is the master node and nodes 1, 2 and 3 are secondary nodes.

Private and Shared Disk Groups

Two types of disk groups are defined:

•Private disk groups (belong to only one node). A private disk group is only imported by one system. Disks in a private disk group may be physically accessible from one or more systems, but access is restricted to one system only. The boot disk group (usually aliased by the reserved disk group name bootdg) is always a private disk group.

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

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