Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

contact with a specific disk, CVM excludes the node from participating in the use
of that disk.
CVM communication
CVM communication involves various GAB ports for different types of
communication. For an illustration of these ports:
CVM communication involves the following GAB ports:
■ Port w
Most CVM communication uses port w for vxconfigd communications. During
any change in volume configuration, such as volume creation, plex attachment
or detachment, and volume resizing, vxconfigd on the master node uses port
w to share this information with slave nodes.
When all slaves use port w to acknowledge the new configuration as the next
active configuration, the master updates this record to the disk headers in the
VxVM private region for the disk group as the next configuration.
■ Port v
CVM uses port v for kernel-to-kernel communication. During specific
configuration events, certain actions require coordination across all nodes.
An example of synchronizing events is a resize operation. CVM must ensure
all nodes see the new or old size, but never a mix of size among members.
CVM also uses this port to obtain cluster membership from GAB and determine
the status of other CVM members in the cluster.
■ Port u
CVM uses the group atomic broadcast (GAB) transport mechanism of VCS to
ship the commands from the slave node to the master node. CVM uses group
atomic broadcast (GAB) port u.
CVM processes one node joining the cluster at a time. If multiple nodes want
to join the cluster simultaneously, each node attempts to open port u in
exclusive mode. (GAB only allows one node to open a port in exclusive mode).
As each node joins the cluster, GAB releases the port. The next node can then
open the port and join the cluster. In a case of multiple nodes, each node
continuously retries at pseudo-random intervals until it wins the port.
CVM recovery
When a node leaves a cluster, the new membership is delivered by GAB, to CVM
on existing cluster nodes. The fencing driver (VXFEN) ensures that split-brain
scenarios are taken care of before CVM is notified. CVM then initiates recovery
of mirrors of shared volumes that might have been in an inconsistent state
following the exit of the node.
31Overview of Veritas Storage Foundation for Oracle RAC
Component products and processes of SF Oracle RAC