VERITAS Volume Manager 3.1 Administrator's Guide
Disk Group Tasks
Disk Groups
Chapter 5 209
Disk Groups
Disks are organized by the Volume Manager into disk groups. A
disk
group
is a named collection of disks that share a common configuration.
Volumes are created within a diskgroup and are restricted to using disks
within that disk group.
A system with the Volume Manager installed has the default disk group,
rootdg. By default, operations are directed to the rootdg disk group.
The system administrator can create additional disk groups as
necessary. Many systems do not use more than one disk group, unless
they have a large number of disks. Disks are not added to disk groups
until the disks are needed to create Volume Manager objects. Disks can
be initialized, reserved, and added to disk groups later. However, at least
one disk must be added to rootdg for you to do the Volume Manager
installation procedures.
Even though the rootdg is the default disk group, it is not the root disk
group. In the current release the root volume group is always under LVM
control.
When a disk is added to a disk group, it is given a name (for example,
disk02). This name identifies a disk for volume operations: volume
creation or mirroring. This name relates directly to the physical disk. If a
physical disk is moved to a different target address or to a different
controller, the name disk02 continues to refer to it. Disks can be
replaced by first associating a different physical disk with the name of
the disk to be replaced and then recovering any volume data that was
stored on the original disk (from mirrors or backup copies).
Having large disk groups can cause the private region to fill. In the case
of larger disk groups, disks should be set up with larger private areas to
log in. A major portion of a private region is space for a disk group
configuration database containing records for each Volume Manager
object in that disk group. Because each configuration record takes up 256
bytes (or half a block), the number of records that can be created in a
disk group is twice the configuration database copy size. The copy size
can be obtained from the output of the command vxdg list
diskgroupname
.
You may wish to add a new disk to an already established disk group. For
example, the current disks may have insufficient space for the project or
work group requirements, especially if these requirements have