Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

27Understanding Veritas Volume Manager
How VxVM handles storage management
In releases prior to VxVM 4.0, the default disk group was rootdg (the root disk group).
For VxVM to function, the rootdg disk group had to exist and it had to contain at least
one disk. This requirement no longer exists, and VxVM can work without any disk groups
configured (although you must set up at least one disk group before you can create any
volumes of otherVxVM objects). For more information about changes to disk group
configuration, see “Creating and administering disk groups” on page 157.
You can create additional disk groups when you need them. Disk groups allow you to
group disks into logical collections. A disk group and its components can be moved as a
unit 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 187.
Volumes are created within a disk group. A given volume and its plexes and subdisks
must be configured from disks in the same disk group.
VM disks
When you place a physical disk under VxVM control, a VM disk is assigned to the
physical disk. A VM disk is under VxVM control and is usually in a disk group. Each VM
disk corresponds to one physical disk. VxVM allocates storage from a contiguous area of
VxVM disk space.
A VM disk typically includes a public region (allocated storage) and a small private
region where VxVM internal configuration information is stored.
Each VM disk has a unique disk media name (a virtual disk name). You can either define a
disk name of up to 31 characters, or allow VxVM to assign a default name that takes the
form diskgroup##, where diskgroup is the name of the disk group to which the disk
belongs (see “Disk groups” on page 26).
Figure 1-6 shows a VM disk with a media name of disk01 that is assigned to the
physical disk devname.
Figure 1-6 VM disk example
devname
VM disk
Physical disk
disk01