VERITAS Volume Manager 4.1 Administrator's Guide

Administering Cluster Functionality

Overview of Cluster Volume Management

Chapter 10358

NOTE If the default activation node is anything other than off, an activation

following a cluster join, or a disk group creation or import can fail if

another node in the cluster has activated the disk group in a conﬂicting

mode.

To display the activation mode for a shared disk group, use the vxdg

list diskgroup command as described in “Listing Shared Disk Groups”

on page 372.

You can also use the vxdg command to change the activation mode on a

shared disk group as described in “Changing the Activation Mode on a

Shared Disk Group” on page 377.

For a description of how to conﬁgure a volume so that it can only be

opened by a single node in a cluster, see “Creating Volumes with

Exclusive Open Access by a Node” on page 377 and “Setting Exclusive

Open Access to a Volume by a Node” on page 378.

Connectivity Policy of Shared Disk Groups

The nodes in a cluster must always agree on the status of a disk. In

particular, if one node cannot write to a given disk, all nodes must stop

accessing that disk before the results of the write operation are returned

to the caller. Therefore, if a node cannot contact a disk, it should contact

another node to check on the disk’s status. If the disk fails, no node can

access it and the nodes can agree to detach the disk. If the disk does not

fail, but rather the access paths from some of the nodes fail, the nodes

cannot agree on the status of the disk. Either of the following policies for

resolving this type of discrepancy may be applied:

• Under the global connectivity policy, the detach occurs cluster-wide

(globally) if any node in the cluster reports a disk failure. This is the

default policy.

• Under the local connectivity policy, in the event of disks failing, the

failures are conﬁned to the particular nodes that saw the failure.

Note that an attempt is made to communicate with all nodes in the

cluster to ascertain the disks’ usability. If all nodes report a problem

with the disks, a cluster-wide detach occurs.