Veritas 5.0.1 Installation Guide, HP-UX 11i v3, First Edition, November 2009

VxVM Objects
VxVM supports the following types of objects:
• Physical Objects
Physical disks or other hardware with block and raw operating system device interfaces
that are used to store data.
• Virtual Objects
The virtual objects in VxVM include the following:
— Disk Group
A group of disks that share a common configuration. A configuration consists of a set
of records describing objects (including disks, volumes, plexes, and subdisks) that are
associated with one particular disk group. Each disk group has an administrator-assigned
name, which can be used by the administrator to reference that disk group. Each disk
group also has an internally defined unique disk group ID, which is used to differentiate
two disk groups with the same administrator-assigned name.
— VM Disks
When you place a physical disk under VxVM control, a VM disk is assigned to the
physical disk. Each VM disk corresponds to one physical disk. A VM disk is under
VxVM control and is usually in a disk group.
— Subdisks
A VM disk can be divided into one or more subdisks. Each subdisk represents a specific
portion of a VM disk, which in turn is mapped to a specific region in a physical disk.
VxVM allocates a set of contiguous blocks for a subdisk.
— Plexes
VxVM uses subdisks to build virtual objects called plexes. A plex consists of one or
more subdisks located on one or more physical disks.
— Volumes
A volume is a virtual disk device that appears like a physical disk device to applications,
databases, and file systems. However, VxVM volumes do 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.
Volume Layouts in VxVM
A volume layout is defined by the association of a volume to one or more plexes, each of which
maps to a subdisk. VxVM supports two different types of volume layout:
• Non-Layered
• Layered
Non-Layered
In a non-layered volume layout, a subdisk maps directly to a VM disk. This enables the subdisk
to define a contiguous extent of storage space backed by the public region of a VM disk.
Layered Volumes
A layered volume is constructed by mapping its subdisks to the underlying volumes. The subdisks
in the underlying volumes must map to VM disks, and hence to the attached physical storage.
Veritas Volume Manager (VxVM) 17