Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Cluster Initialization and Configuration
362 VERITAS Volume Manager Administrator’s Guide
new disk group with the same name as an existing disk group. The vxconfigd daemon
on the master node then sends details of the changes to the vxconfigd daemons on the
slave nodes. The vxconfigd daemons on the slave nodes then perform their own
checking. For example, each slave node checks that it does not have a private disk group
with the same name as the one being created; if the operation involves a new disk, each
node checks that it can access that disk. When the vxconfigd daemons on all the nodes
agree that the proposed change is reasonable, each notifies its kernel. The kernels then
co-operate to either commit or to abandon the transaction. Before the transaction can be
committed, all of the kernels ensure that no I/O is underway. The master node is
responsible both for initiating the reconfiguration, and for coordinating the commitment
of the transaction. The resulting configuration changes appear to occur simultaneously on
all nodes.
If a vxconfigd daemon on any node goes away during reconfiguration, all nodes are
notified and the operation fails. If any node leaves the cluster, the operation fails unless
the master has already committed it. If the master node leaves the cluster, the new master
node, which was previously a slave node, completes or fails the operation depending on
whether or not it received notification of successful completion from the previous master
node. This notification is performed in such a way that if the new master does not receive
it, neither does any other slave.
If a node attempts to join a cluster while a volume reconfiguration is being performed, the
result of the reconfiguration depends on how far it has progressed. If the kernel has not
yet been invoked, the volume reconfiguration is suspended until the node has joined the
cluster. If the kernel has been invoked, the node waits until the reconfiguration is
complete before joining the cluster.
When an error occurs, such as when a check on a slave fails or a node leaves the cluster,
the error is returned to the utility and a message is sent to the console on the master node
to identify on which node the error occurred.
vxconfigd Daemon
The VxVM configuration daemon, vxconfigd, maintains the configuration of VxVM
objects. It receives cluster-related instructions from the kernel. A separate copy of
vxconfigd runs on each node, and these copies communicate with each other over a
network. When invoked, a VxVM utility communicates with the vxconfigd daemon
running on the same node; it does not attempt to connect with vxconfigd daemons on
other nodes. During cluster startup, the kernel prompts vxconfigd to begin cluster
operation and indicates whether it is a master node or a slave node.