VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 10, Administering Cluster Functionality
Cluster Initialization and Configuration
253
If other operations, such as VxVM operations or recoveries, are in progress, cluster
reconfiguration can be delayed until those operations have completed. Volume
reconfigurations (see “Volume Reconfiguration” on page 254) do not take place at the
same timeas clusterreconfigurations. Depending onthe circumstances, an operationmay
be held up and restarted later. In most cases, cluster reconfiguration takes precedence.
However, if the volume reconfiguration is in the commit stage, it completes first.
For more information on cluster reconfiguration, see “vxclustd Daemon.”
vxclustd Daemon
The vxclustd daemon is the VxVM cluster reconfiguration daemon. The vxclustd
daemon provides communication between the cluster monitor and VxVM, and initiates
cluster reconfiguration. Every node currently in the cluster runs an instance of the
vxclustd daemon. Whenever cluster membership changes, the cluster monitor notifies
the vxclustd daemon, which then initiates a reconfiguration within VxVM.
The vxclustd daemon is started up by the cluster monitor when the node initially
attempts tojoin thecluster. Thevxclustd daemon first registerswith the cluster monitor
and obtains the following information from the cluster monitor:
◆ cluster ID and cluster name
◆ node IDs and hostnames of all configured nodes
◆ IP addresses of the network interfaces through which the nodes communicate with
each other
Registration also sets up a callback mechanism for the cluster monitor to notify the
vxclustd daemon when cluster membership changes. After initializing kernel cluster
variables, the vxclustd daemon waits for a callback from the cluster monitor. When the
vxclustd daemon obtainsmembership informationfromthe cluster monitor, itvalidates
the membership change, and provides the new membership to the kernel. The
reconfiguration process continues within the kernel and the vxconfigd daemon. This
includes selection ofa newmaster nodeif necessary, initiationof communicationbetween
vxconfigd daemons on the master and slave nodes, and a join protocol at the
vxconfigd and kernel levels that validates VxVM objects and distributes VxVM
configuration information across the cluster.
If reconfiguration completes successfully, the vxclustd daemon does not take any
further action; it waits for the next membership change from the cluster monitor. If
reconfiguration within the kernel or within the vxconfigd daemon fails, the node must
leave the cluster. The kernel fails I/O in progress to shared disks, and stops access to
shared disks and the vxclustd daemon. The vxclustd daemon invokes the cluster
monitor command to halt the cluster on this node.
When a clean node shutdown is performed, vxclustd waits until kernel cluster
reconfiguration completes and then exits.