Veritas Volume Manager VxVM operates as a subsystem between your operating system and your data management systems, such as file systems and database management systems.
Hard disks are formatted, and information stored, using two methods: physical-storage layout and logical-storage layout.
Physical objects—physical disks or other hardware with block and raw operating system device interfaces that are used to store data.
Virtual objects—When one or more physical disks are brought under the control of VxVM, it creates virtual objects called volumes on those physical disks.
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Veritas Cluster Server (VCS) from Symantec connects multiple, independent
systems into a management framework for increased availability. Each system,
or node, runs its own operating system and cooperates at the software level to
form a cluster. VCS links commodity hardware with intelligent software to
provide application failover and control. When a node or a monitored
application fails, other nodes can take predefined actions to take over and bring
up services elsewhere in the cluster.
VCS detects failure of an application by issuing specific commands, tests, or
scripts to monitor the overall health of an application. VCS also determines the
health of underlying resources supporting the application, such as file systems
and network interfaces.
VCS uses a redundant network heartbeat to discriminate between the loss of a
system and the loss of communication between systems. VCS also uses
SCSI3-based membership coordination and data protection for detecting failure
on a node and on fencing.
About switchover and failover
Switchover and failover are the processes of bringing up application services on
a different node in a cluster.
Switchover A switchover is an orderly shutdown of an application and its supporting resources on one server and a controlled startup on another server.
Failover A failover is similar to a switchover, except the ordered shutdown of
applications on the original node may not be possible, so the services are
started on another node.