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 play an active role in volume reconfiguration. For reconfiguration to succeed, a
vxconfigd daemon must be running on each of the nodes.
See "vxconfigd daemon" on page 415.
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. 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.
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.
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.
TWhen a node is initialized for cluster operation, the
vxconfigd daemon is notified that the node is about to join the cluster and is provided with the following information from the cluster monitor configuration database:
vxconfigddaemon on each node (if applicable)
On the master node, the
vxconfigd daemon sets up the shared configuration by importing shared disk groups, and informs the kernel when it is ready for the slave nodes to join the cluster.
On slave nodes, the
vxconfigd daemon is notified when the slave node can join the cluster. When the slave node joins the cluster, the
vxconfigd daemon and the VxVM kernel communicate with their counterparts on the master node to set up the shared configuration.
When a node leaves the cluster, the kernel notifies the
vxconfigd daemon on all the other nodes. The master node then performs any necessary cleanup. If the master node leaves the cluster, the kernels select a new master node and the
vxconfigd daemons on all nodes are notified of the choice.
vxconfigd daemon also participates in volume reconfiguration.
See "Volume reconfiguration" on page 414.
In a cluster, the
vxconfigd daemons on the slave nodes are always connected to the
vxconfigd daemon on the master node. If the
vxconfigd daemon is stopped, volume reconfiguration cannot take place. Other nodes can join the cluster if the
vxconfigd daemon is not running on the slave nodes.
vxconfigd daemon stops, different actions are taken depending on which node this occurred:
vxconfigddaemon is stopped on the master node, the
vxconfigddaemons on the slave nodes periodically attempt to rejoin to the master node. Such attempts do not succeed until the
vxconfigddaemon is restarted on the master. In this case, the
vxconfigddaemons on the slave nodes have not lost information about the shared configuration, so that any displayed configuration information is correct.
vxconfigddaemon is stopped on a slave node, the master node takes no action. When the
vxconfigddaemon is restarted on the slave, the slave
vxconfigddaemon attempts to reconnect to the master daemon and to re-acquire the information about the shared configuration. (Neither the kernel view of the shared configuration nor access to shared disks is affected.) Until the
vxconfigddaemon on the slave node has successfully reconnected to the
vxconfigddaemon on the master node, it has very little information about the shared configuration and any attempts to display or modify the shared configuration can fail. For example, shared disk groups listed using the
listcommand are marked as
disabled; when the rejoin completes successfully, they are marked as
vxconfigddaemon is stopped on both the master and slave nodes, the slave nodes do not display accurate configuration information until
vxconfigdis restarted on the master and slave nodes, and the daemons have reconnected.
If the CVM agent for VCS determines that the
vxconfigd daemon has stopped on a node,
vxconfigd is restarted automatically.
-rreset option to
vxconfigddaemon and recreates all states from scratch. This option cannot be used to restart
vxconfigdwhile a node is joined to a cluster because it causes cluster information to be discarded.
It may sometimes be necessary to restart
vxconfigd manually in a VCS controlled cluster to resolve a VxVM issue.
To restart vxconfigd manually
hagrp -freeze group
hagrp -unfreeze group