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

Chapter 1, Understanding VERITAS Volume Manager
Device Discovery
9
Disk Groups
A disk group is a collection of VM disks that share a common configuration. A disk group
configuration is a set of records with detailed information about related VxVM objects,
their attributes, and their connections. The default disk group is rootdg (or root disk
group). A disk group name can be up to 31 characters long.
Note Even though rootdg is the default disk group, it does not necessarily contain the
root disk. In the current release, the root disk may be under VxVM or LVM control.
You can create additional disk groups as necessary. Disk groups allow you to group disks
into logicalcollections. A diskgroup and its components can bemoved as aunit from one
host machine to another. The ability to move whole volumes and disks between disk
groups, to split whole volumes and disks between disk groups, and to join disk groups is
described in “Reorganizing the Contents of Disk Groups” on page 121.
Volumes are created within a disk group. A given volume must be configured from disks
in the same disk group.
Subdisks
A subdisk is a set of contiguous disk blocks. A block is a unit of space on the disk. VxVM
allocates disk space using subdisks. A VM disk can be divided into one or more subdisks.
Each subdisk represents a specific portion of a VM disk, which is mapped to a specific
region of a physical disk.
The default name for a VM disk is disk## (such as disk01) and the default name for a
subdisk is disk##-##. In the figure, “Subdisk Example”, disk01-01 is the name of
the first subdisk on the VM disk named disk01.
Subdisk Example
A VM disk can contain multiple subdisks, but subdisks cannot overlap or share the same
portions of a VM disk. “Example of Three Subdisks Assigned to One VM Disk” shows a
VM disk with three subdisks. The VM disk is assigned to one physical disk.
SubdiskVM Disk with One Subdisk
disk01-01 disk01-01
disk01