Coordination points provide a lock mechanism to determine which nodes get to fence off data drives from other nodes. A node must eject a peer from the coordination points before it can fence the peer from the data drives. Racing for control of the coordination points to fence data disks is the key to understand how fencing prevents split brain.
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.
Dynamic Multipathing (DMP) allows coordinator disks to take advantage of the path failover and the dynamic adding and removal capabilities of DMP. On cluster nodes with HP-UX 11i v3, you must use DMP devices or iSCSI devices for I/O fencing. The following changes in HP-UX 11i v3 require you to not use raw devices for I/O fencing:
The metanode interface that HP-UX provides does not meet the SCSI-3 PR requirements for the I/O fencing feature. You can configure coordinator disks to use Veritas Volume Manager Dynamic Multipathing (DMP) feature.