VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality

Cluster Functionality Overview

Chapter 7 301

Any reconﬁguration to a shared disk group is performed with the

cooperation of all nodes. Conﬁguration changes to the disk group happen

simultaneously on all nodes and the changes are identical. These

changes are atomic in nature, so they either occur simultaneously on all

nodes or do not occur at all.

All members of the cluster can have simultaneous read and write access

to any cluster-shareable disk group depending on the activation mode.

Access by the active nodes of the cluster is not affected by a failure in any

other node. The data contained in a cluster-shareable disk group is

available as long as at least one node is active in the cluster. Regardless

of which node accesses the cluster-shareable disk group, the

conﬁguration of the disk group looks the same. Applications running on

each node can access the data on the VM disks simultaneously.

NOTE VxVM does not protect against simultaneous writes to shared volumes

by more than one node. It is assumed that any consistency control is

done at the application level (using a distributed lock manager, for

example).

Conﬁguration & Initialization

Before any nodes can join a new cluster for the ﬁrst time, the system

administrator must supply certain conﬁguration information. This

information is supplied during cluster manager setup and is normally

stored in some type of cluster manager conﬁguration database. The

precise content and format of this information is dependent on the

characteristics of the cluster manager. Information required by VxVM is

as follows:

• cluster ID

• node IDs

• network addresses of nodes

• port addresses

When a node joins the cluster, this information is automatically loaded

into VxVM on that node at node startup time.

NOTE If MC/ServiceGuard is chosen as your cluster manager, no additional