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413Administering cluster functionality
Cluster initialization and configuration
See the vxclustadm(1M) manual page for more information about vxclustadm
and for examples of its usage.
Volume reconfiguration
Volume reconfiguration is the process of creating, changing, and removing
VxVM objects such as disk groups, volumes and plexes. In a cluster, all nodes
co-operate to perform such operations. The vxconfigd daemons (see
“vxconfigd daemon” on page 414) play an active role in volume reconfiguration.
For reconfiguration to succeed, a vxconfigd daemon must be running on each
of the nodes.
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.