Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Planning and Documenting an HA Cluster
Cluster Lock Planning
Chapter 4 101
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 42.
For information about configuring a lock LUN or a quorum server into
the cluster, see “Quorum Server Information” on page 106, “Specifying a
Quorum Server” on page 180, “Lock LUN Information” on page 106, and
“Specifying a Lock LUN” on page 180.
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 more information setting up a lock LUN or a Quorum Server, see
“Setting up the Quorum Server” on page 151 and “Setting up the Lock
LUN” on page 154.
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.
Using a Quorum Server
The Quorum Server is described in detail under “Use of the Quorum
Server as a Cluster Lock” on page 43. See also “Cluster Lock” on page 42.
A quorum server: