One of the new features introduced in Sun Cluster 3.2 was the Quorum server. The objective was to provide alternatives to the existing (and preferred method) method that makes use of shared disks. The Quorum server can be a stand alone node running Solaris 8/9/10. It is recommended that the Quorum server resides in the same subnet as the cluster so that any network issue doesn't cause a cluster outage because of lack of quorum.
Quorum server is very useful where shared disks are not preferred. The Quorum Server software can be installed from the Sun Cluster dvd and doesn't have much dependencies other than the shared components. Once the pkgs are installed, the configuration file with default values is created - /etc/scqsd/scqsd.conf. The default port is 9000 and there can be multiple quorum servers running on the same node. Exercise caution in this regard as if the quorum server goes down, more clusters get affected!
The quorum server can be started manually using the following command format:
/usr/cluster/bin/clquorumserver start quorumserver
The value of quorumserver is the instance name provided in the configuration file.
Once the quorum server is configured, its service can be availed by adding it to the cluster using the interactive clsetup menu.
bash-3.00# clsetup
*** Main Menu ***
Please select from one of the following options:
1) Quorum
2) Resource groups
3) Data Services
4) Cluster interconnect
5) Device groups and volumes
6) Private hostnames
7) New nodes
8) Other cluster tasks
?) Help with menu options
q) Quit
Option: 1
*** Quorum Menu ***
Please select from one of the following options:
1) Add a quorum device
2) Remove a quorum device
?) Help
q) Return to the Main Menu
Option: 1
>>> Add a Quorum Device <<<
This option is used to add a quorum device to the cluster
configuration. Quorum devices are necessary to protect the cluster
from split brain and amnesia situations. Each quorum device must be
connected to at least two nodes. You can use a device containing user
data.
Adding a quorum device automatically configures node-to-device paths
for the nodes attached to the device. Later, if you add more nodes to
the cluster, you might need to update these paths by removing then
adding back the quorum device. For more information on supported
quorum device topologies, see the Sun Cluster documentation.
Is it okay to continue (yes/no) [yes]?
What is the type of device you want to use?
1) Directly attached shared disk
2) Network Attached Storage (NAS) from Network Appliance
3) Quorum Server
q) Return to the quorum menu
Option: 3
>>> Add a Quorum Server Quorum Device <<<
A Quorum Server process runs on a machine outside Sun Cluster and
serves the cluster as a quorum device. Before configuring the quorum
server as a quorum device into the cluster, you will need to setup the
quorum server machine and start the quorum server process. For
detailed information on setting up a quorum server, refer to Sun
Cluster system administration guide.
You will need to specify a device name for the quorum server quorum
device, which must be unique across all quorum devices, the IP address
of the quorum server machine, or hostname if the machine is added into
/etc/hosts, and a port number on the quorum server machine used to
communicate with the cluster nodes. Please refer to the clquorum(1M)
man page and other Sun Cluster documentation for details.
Is it okay to continue (yes/no) [yes]?
What name do you want to use for this quorum device? test
What is the IP address of the quorum server machine? xxxxxx
What is the port number on the quorum server machine? 9000
Is it okay to proceed with the update (yes/no) [yes]?
clquorum add -t quorum_server -p qshost=xxxxxx -p port=9000 test
Command completed successfully.
You can verify the output with the clq status <instance-name> command.
bash-3.00# clq status test
=== Cluster Quorum ===
--- Quorum Votes by Device ---
Device Name Present Possible Status
----------- ------- -------- ------
test 1 1 Online
As simple as that! 
The documentation can be found at Configuring the Sun Cluster Quorum Server Software.
