Veritas 5.0 Installation Guide, HP-UX 11i v3, First Edition, May 2008

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.
VxVM Storage Layouts
Data in virtual objects is organized to create volumes by using the following layouts:
• Concatenation and Spanning
• Striping (RAID-0)
• Mirroring (RAID-1)
• Striping Plus Mirroring (Mirrored-Stripe or RAID-0+1)
• Mirroring Plus Striping (Striped-Mirror, RAID-1+0 or RAID-10)
• RAID-5 (Striping with Parity)
Concatenation and Spanning
Concatenation maps data in a linear manner onto one or more subdisks in a plex. To access the
data in a concatenated plex sequentially, data is first accessed from the first subdisk from
beginning to end and then accessed in the remaining subdisks sequentially from beginning to
end, until the end of the last subdisk.
16 Introduction