VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Layered Volumes
Chapter 154
Layered Volumes
Another Volume Manager virtual object is the layered volume. A
layered volume is built on top of volume(s). The layered volume structure
tolerates failure better and has greater redundancy than the standard
volume structure. For example, in a striped and mirrored layered
volume, each mirror (plex) covers a smaller area of storage space, so
recovery is quicker than with a standard mirror volume. Figure 1-19,
Example of a Striped-Mirrored Layered Volume, shows an example
layered volume design.
In Figure 1-19, Example of a Striped-Mirrored Layered Volume,,
illustrates how the volume and striped plex in the “User Manipulation”
area allow you to perform normal Volume Manager tasks. User tasks can
be performed only on the top-level volume of a layered volume. You
cannot detach a layered volume or perform any other operation on the
underlying volumes by manipulating the internal structure. You can
perform all necessary operations from the user manipulation area that
includes the volume and striped plex (for example, to change the column
width, or to add a column).
The “Volume Manager Manipulation” area shows subdisks with two
columns, built on underlying volumes with each volume internally
mirrored. Layered volumes are an infrastructure within Volume
Manager and they allow the addition of certain features to be added to
Volume Manager. Underlying volumes are used exclusively by the
Volume Manager and are not designed for user manipulation. The
underlying volume structure is described here to help you understand
how layered volumes work and why they are used by Volume Manager.