Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

■ Private and shared disk groups

■ Activation modes of shared disk groups

■ Connectivity policy of shared disk groups

■ Limitations of shared disk groups

Private and shared disk groups

Table 2-3 describes the disk group types.

Table 2-3

Disk group types

DescriptionDisk group

Belongs 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 import is restricted to one system only.

The root disk group is always a private disk group.

Private

Is 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.

Shared

In a cluster, most disk groups are shared. Disks in a shared disk group are

accessible from all nodes in a cluster, allowing applications on multiple cluster

nodes to simultaneously access the same disk. A volume in a shared disk group

can be simultaneously accessed by more than one node in the cluster, subject to

licensing and disk group activation mode restrictions.

You can use the vxdg command to designate a disk group as cluster-shareable.

When a disk group is imported as cluster-shareable for one node, each disk header

is marked with the cluster ID. As each node subsequently joins the cluster, it

recognizes the disk group as being cluster-shareable and imports it. You can also

import or deport a shared disk group at any time; the operation takes places in a

distributed fashion on all nodes.

Each physical disk is marked with a unique disk ID. When cluster functionality

for VxVM starts on the master, it imports all shared disk groups (except for any

that have the noautoimport attribute set). When a slave tries to join a cluster, the

master sends it a list of the disk IDs that it has imported, and the slave checks to

see if it can access them all. If the slave cannot access one of the listed disks, it

abandons its attempt to join the cluster. If it can access all of the listed disks, it

imports the same shared disk groups as the master and joins the cluster. When a

node leaves the cluster, it deports all its imported shared disk groups, but they

remain imported on the surviving nodes.

Storage Foundation Cluster File System architecture

About Veritas Volume Manager cluster functionality