Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Volumes
A volume is a virtual disk device that appears to applications, databases, and file
systems like a physical disk device, but does not have the physical limitations of
a physical disk device. A volume consists of one or more plexes, each holding a
copy of the selected data in the volume. Due to its virtual nature, a volume is not
restricted to a particular disk or a specific area of a disk. The configuration of a
volume can be changed by using VxVM user interfaces. Configuration changes
can be accomplished without causing disruption to applications or file systems
that are using the volume. For example, a volume can be mirrored on separate
disks or moved to use different disk storage.
VxVM uses the default naming conventions of vol## for volumes and vol##-##
for plexes in a volume. For ease of administration, you can choose to select more
meaningful names for the volumes that you create.
A volume may be created under the following constraints:
■ Its name can contain up to 31 characters.
■ It can consist of up to 32 plexes, each of which contains one or more subdisks.
■ It must have at least one associated plex that has a complete copy of the data
in the volume with at least one associated subdisk.
■ All subdisks within a volume must belong to the same disk group.
Figure 1-10 shows a volume vol01 with a single plex.
Figure 1-10
Example of a volume with one plex
Volume with one plex
Plex with one subdisk
vol01
vol01-01
vol01-01
disk01-01
The volume vol01 has the following characteristics:
■ It contains one plex named vol01-01.
■ The plex contains one subdisk named disk01-01.
■ The subdisk disk01-01 is allocated from VM disk disk01.
Figure 1-11 shows a mirrored volume, vol06, with two data plexes.
33Understanding Veritas Volume Manager
How VxVM handles storage management