Managing Serviceguard Eighteenth Edition, September 2010

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 ” (page 62).
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” (page 225), “Setting Up a Lock LUN” (page 226), and “Setting Up
and Running the Quorum Server” (page 230).
Cluster Lock Disk and Re-formation Time
cmquerycl (1m) 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 ” (page 128).
Planning for Expansion
Bear in mind that a cluster with more than 4 nodes cannot use a lock disk or lock LUN.
Thus, 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 operation of Quorum Server is described under “Use of the Quorum Server as the
Cluster Lock” (page 65). See also “Cluster Lock ” (page 62), “Specifying a Quorum
Server” (page 248), and the QS_HOST and QS_ADDR parameter descriptions under
“Cluster Configuration Parameters ” (page 143).
130 Planning and Documenting an HA Cluster