VERITAS Volume Manager 4.1 Administrator's Guide

Administering Disks
Disk Devices
Chapter 266
Private and Public Disk Regions
A VM disk usually has two regions:
private region A small area where configuration information is stored. A disk header label,
configuration records for VxVM objects (such as volumes, plexes and
subdisks), and an intent log for the configuration database are stored here.
The default private region size is 2048 blocks (2048 kilobytes), which is
large enough to record the details of about 4000 VxVM objects in a disk
group.
Under most circumstances, the default private region size should be
sufficient. For administrative purposes, it is usually much simpler to create
more disk groups that contain fewer volumes, or to split large diskgroups
into several smaller ones (as described in “Splitting Disk Groups” on
page 183). If required, the value for the private region size may be
overridden when you add or replace a disk using the vxdiskadm command.
Each disk that has a private region holds an entire copy of the configuration
database for the disk group. The size of the configuration database for a disk
group is limited by the size of the smallest copy of the configuration
database on any of its member disks.
public region An area that covers the remainder of the disk, and which is used for the
allocation of storage space to subdisks.
A disk’s type identifies how VxVM accesses a disk, and how it manages the disk’s private and
public regions. The following basic disk types are used by VxVM:
simple The public and private regions are on the same disk area (with the public
area following the private area).
nopriv There is no private region (only a public region for allocating subdisks). This
is the simplest disk type consisting only of space for allocating subdisks.
Such disks are most useful for defining special devices (such as RAM disks,
if supported) on which private region data would not persist between
reboots. They can also be used to encapsulate disks where there is
insufficient room for a private region. The disks cannot store configuration
and log copies, and they do not support the use of the vxdisk addregion
command to define reserved regions. VxVM cannot track the movement of
nopriv disks on a SCSI chain or between controllers.
auto When the vxconfigd daemon is started, VxVM obtains a list of known disk
device addresses from the operating system and configures disk access
records for them automatically.
Auto-configured disks (with disk access type auto) support the following disk formats: