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

159Creating and administering disk groups
Specifying a disk group to commands
System-wide reserved disk groups
The following disk group names are reserved, and cannot be used to name any disk groups
that you create:
bootdg Specifes the boot disk group. This is an alias for the disk group that
contains the volumes that are used to boot the system. VxVM sets bootdg
to the appropriate disk group if it takes control of the root disk. Otherwise,
bootdg is set to nodg (no disk group; see below).
Caution: Do not attempt to change the assigned value of bootdg. Doing so may render
your system unbootable.
defaultdg Specifies the default disk group. This is an alias for the disk group name
that should be assumed if the -g option is not specified to a command, or if
the VXVM_DEFAULTDG environment variable is undefined. By default,
defaultdg is set to nodg (no disk group; see below).
nodg Specifies to an operation that no disk group has been defined. For example,
if the root disk is not under VxVM control, bootdg is set to nodg.
Note: If you have upgraded your system, you may find it convenient to continue to
configure a disk group named rootdg as the default disk group (defaultdg). There is
no requirement that both defaultdg and bootdg refer to the same disk group, nor that
either the default disk group or the boot disk group be named rootdg.
Rules for determining the default disk group
It is recommended that you use the -g option to specify a disk group to VxVM commands
that accept this option. If you do not specify the disk group, VxVM applies the following
rules in order until it determines a disk group name:
■ Use the default disk group name that is specified by the environment variable
VXVM_DEFAULTDG. This variable can also be set to one of the reserved system-wide
disk group names: bootdg, defaultdg, or nodg. If the variable is undefined, the
following rule is applied.
■ Use the disk group that has been assigned to the system-wide default disk group alias,
defaultdg. See “Displaying and specifying the system-wide default disk group”
on page 160. If this alias is undefined, the following rule is applied.
■ If the operation can be performed without requiring a disk group name (for example,
an edit operation on disk access records), do so.
If none of these rules succeeds, the requested operation fails.