Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

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Creating and Administering Disk Groups
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This chapter describes how to create and manage disk groups. Disk groups are named
collections of disks that share a common configuration. Volumes are created within a disk
group and are restricted to using disks within that disk group.
Note In releases of VERITAS Volume Manager (VxVM) prior to 4.0, a system installed
with VxVM was configured with a default disk group, rootdg, that had to contain
at least one disk. By default, operations were directed to the rootdg disk group.
From release 4.0 onward, VxVM can function without any disk group having been
configured. Only when the first disk is placed under VxVM control must a disk
group be configured. There is no longer a requirement that you name any disk
group rootdg, and any disk group that is named rootdg has no special properties
because of this name. See “Specifying a Disk Group to Commands” on page 132 for
more information about using disk group names that are reserved for special
purposes.
Additionally, prior to VxVM 4.0, some commands such as vxdisk were able to
deduce the disk group if the name of an object was uniquely defined in one disk
group among all the imported disk groups. Resolution of a disk group in this way is
no longer supported for any command.
For a discussion of disk groups that are compatible with the Cross-platform Data
Sharing (CDS) feature of VERITAS Volume Manager, see the VERITAS Storage
Foundation Cross-Platform Data Sharing Administrator’s Guide. The CDS feature allows
you to move VxVM disks and objects between machines that are running under
different operating systems.
As system administrator, you can create additional disk groups to arrange your system’s
disks for different purposes. Many systems do not use more than one disk group, unless
they have a large number of disks. Disks can be initialized, reserved, and added to disk
groups at any time. Disks need not be added to disk groups until the disks are needed to
create VxVM objects.
When a disk is added to a disk group, it is given a name (for example, mydg02). This
name identifies a disk for operations such as volume creation or mirroring. The name also
relates directly to the underlying physical disk. If a physical disk is moved to a different