Managing Serviceguard Fifteenth Edition, reprinted May 2008

Planning and Documenting an HA Cluster
Cluster Lock Planning
Chapter 4 145
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 an LVM lock disk, a lock LUN, or a quorum server as the cluster
lock. For more information about the cluster lock, and requirements and
recommendations, see “Cluster Lock” on page 68.
NOTE You cannot use more than one type of lock in the same cluster.
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. In selecting a cluster lock configuration, be careful to
anticipate any potential need for additional cluster nodes.
For more information on lock disks, lock LUNs, and the Quorum Server,
see “Choosing Cluster Lock Disks” on page 210, “Setting Up a Lock LUN”
on page 211, and “Setting Up and Running the Quorum Server” on
page 214.
Cluster Lock Disk and Re-formation Time
cmquerycl displays the failover time for the cluster in the Possible
Cluster Lock Devices section, for example:
Possible Cluster Lock Devices:
/dev/dsk/c0t1d4 30 seconds
Note: all lock disks have the same failover time
All disks in all volume groups which are accessible by all nodes in the
cluster are potential cluster lock devices, but because it takes a fixed
amount of time to acquire the cluster lock, regardless of the lock device,
only the first potential lock device is displayed. You may need to choose a
different device because of power considerations; see “Power Supply
Planning” on page 142.