Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

A volume reconfiguration transaction is initiated by running a VxVM utility on
the master node. The utility contacts the local vxconfigd daemon on the master
node, which validates the requested change. For example, vxconfigd rejects an
attempt to create a 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, and block any I/O issued by applications
until the reconfiguration is complete. 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
467Administering cluster functionality
Cluster initialization and configuration