Filter
Top Products
28 Understanding Veritas Volume Manager
How VxVM handles storage management
Veritas Volume Manager, such as data change objects (DCOs), and cache objects,
to provide extended functionality. These objects are discussed later in this
chapter.
Disk groups
A disk group is a collection of disks that share a common configuration, and
which are managed by VxVM (see “VM disks” on page 28). A disk group
configuration is a set of records with detailed information about related VxVM
objects, their attributes, and their connections. A disk group name can be up to
31 characters long.
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 165.
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 195.
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 28).
Figure 1-6 shows a VM disk with a media name of disk01 that is assigned to the
physical disk devname.