VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 1, Understanding VERITAS Volume Manager
Device Discovery
11
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 canbe 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.
Note 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.
See “Example of a Volume with One Plex”.
Example of a Volume with One Plex
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.
A volume with two or more data plexes is “mirrored” and contains mirror images of the
data. See “Example of a Volume with Two Plexes”
Subdisk
Plex
vol01-01
vol01
Volume
disk01-01