Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Planning and Documenting an HA Cluster
Cluster Lock Planning
Chapter 4104
Cluster Lock Planning
The purpose of the cluster lock is to ensure that only one new cluster is
formed in the event that exactly half of the previously clustered nodes
try to form a new cluster. It is critical that only one new cluster is formed
and that it alone has access to the disks specified in its packages. You can
specify a lock LUN or a quorum server as the cluster lock. For more
information about the cluster lock, see“Cluster Lock” on page 46.
NOTE You cannot use more than one type of lock in the same cluster.
Cluster Lock Requirements
A one-node cluster does not require a lock. Two-node clusters require the
use of a cluster lock, and a lock is recommended for larger clusters as
well. Clusters larger than four nodes can use only a quorum server as the
cluster lock.
For information on configuring lock LUNs and the Quorum Server, see
“Setting up a Lock LUN” on page 155, “Specifying a Lock LUN” on
page 173, and the HP Serviceguard Quorum Server Version A.03.00
Release Notes at http://www.docs.hp.com -> High Availability ->
Quorum Server.
Planning for Expansion
Bear in mind that a cluster with more than 4 nodes cannot use a lock
LUN. So if you plan to add enough nodes to bring the total to more than
4, you should use a quorum server.