VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Volume Manager Conceptual Overview
Chapter 1 63
In the 3.0 or higher release of Volume Manager “layered volumes” can be
constructed by permitting the subdisk to map either to a VM disk as
before, or, to a new logical object called a storage volume. A storage
volume provides a recursive level of mapping with layouts similar to the
top-level volume. Eventually, the “bottom” of the mapping requires an
association to a VM disk, and hence to attached physical storage.
Layered volumes allow for more combinations of logical compositions,
some of which may be desirable for configuring a virtual device. Because
permitting free use of layered volumes throughout the command level
would have resulted in unwieldy administration, some ready-made
layered volume configurations have been designed into the 3.0 release of
the Volume Manager.
These ready-made configurations operate with built-in rules to
automatically match desired levels of service within specified
constraints. The automatic configuration is done on a “best-effort” basis
for the current command invocation working against the current
configuration.
To achieve the desired storage service from a set of virtual devices, it
may be necessary to include an appropriate set of VM disks into a disk
group, and to execute multiple configuration commands.
To the extent that it can, Volume Manager handles initial configuration
and on-line re-configuration with its set of layouts and administration
interface to make this job easier.