Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

About coordination points
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.
Note: Typically, a fencing configuration for a cluster must have three coordination
points. Symantec also supports server-based fencing with a single CP server as
its only coordination point with a caveat that this CP server becomes a single
point of failure.
The coordination points can be disks, servers, or both.
■ Coordinator disks
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 SFCFS configuration.
Dynamic Multi-pathing (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:
■ Provides native multipathing support
■ Does not provide access to individual paths through the device file entries
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 Multi-pathing (DMP) feature.
See the Veritas Volume Manager Administrator’s Guide.
■ Coordination point servers
The coordination point server (CP server) is a software solution which runs
on a remote system or cluster. CP server provides arbitration functionality by
allowing the SFCFS cluster nodes to perform the following tasks:
■ Self-register to become a member of an active SFCFS cluster (registered
with CP server) with access to the data drives
■ Check which other nodes are registered as members of this activeSFCFS
cluster
■ Self-unregister from this active SFCFS cluster
Storage Foundation Cluster File System architecture
About I/O fencing
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