HP Veritas Volume Manager 5.0 -UX 11i v3 manual Volume reconfiguration

Administering cluster functionality

Cluster initialization and configuration

413

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.