Symantec Veritas 5 - Manual (Page 89)

Disks that act as coordination points are called coordinator disks. Coordinator
disks are three standard disks or LUNs set aside for I/O fencing during cluster
reconfiguration. Coordinator disks do not serve any other storage purpose in the
VCS configuration.
You can configure coordinator disks to use Veritas Volume Manager Dynamic
Multipathing (DMP) feature. Dynamic Multipathing (DMP) allows coordinator
disks to take advantage of the path failover and the dynamic adding and removal
capabilities of DMP. So, you can configure I/O fencing to use either DMP devices
or the underlying raw character devices. I/O fencing uses SCSI-3 disk policy that
is either raw or dmp based on the disk device that you use. The disk policy is raw
by default. Symantec recommends using the DMP disk policy.
See the Veritas Volume Manager Administrator’s Guide.
About setting up disk-based I/O fencing
Figure 5-1 illustrates the tasks involved to configure I/O fencing.
89 Configuring VCS clusters for data integrity
About setting up disk-based I/O fencing