VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

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Creating and Administering Disk Groups

Introduction

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.

A system with VERITAS Volume Manager (VxVM) installed has a default disk group

conﬁgured, rootdg. By default, operations are directed to the rootdg disk group. 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 are not added to disk groups until the disks are

needed to create VxVM objects. Disks can be initialized, reserved, and added to disk

groups later. However, at least one disk must be added to rootdg when you initially

conﬁgure VxVM after installation.

Note Even though rootdg is the default disk group, it does not contain the root disk. 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. A major portion of a private

region provides space for a disk group conﬁguration database that contains records for

each VxVM object in that disk group. Because each conﬁguration record takes up 256

bytes (orone quarterof a block), the numberof recordsthat can be createdin adisk group

can be estimatedfromthe conﬁgurationdatabase copy size. Thecopy sizein blocks canbe

obtained from the output of the command vxdg list diskgroup as the value of the

permlen parameter on the line starting with the string “config:”. This value is the

smallest of the len values for all copies of the conﬁguration database in the disk group.

The amount of remaining free space in the conﬁguration database is shownas thevalue of