VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Volume Manager Conceptual Overview
Chapter 162
• How does the operating system view the paths?
• How does Volume Manager DMP view the paths?
• How does the Multipathing target deal with their paths?
References Additional information about DMP can be found in this
document in the following sections:
• “Dynamic Multipathing (DMP)”
• “vxdctl Daemon”
• Chapter 4, Disk Tasks,
“Displaying Multipaths Under a VM Disk”
Related information also appears in the following sections of the
Volume Manager Reference Guide:
• “Volume Manager Commands”
• “DMP Error Messages”
• “Multipathed Disk Arrays”
Volume Manager Layouts
A Volume Manager virtual device is defined by a volume. A volume has a
layout defined by the association of a volume to one or more plexes,
which in turn, each map to subdisks. The volume then presents a virtual
device interface exposed to Volume Manager clients for data access.
These logical building blocks re-map the volume address space through
which I/O is re-directed at run-time.
Different volume layouts each provide different levels of storage service.
A volume layout can be configured and re-configured to match particular
levels of desired storage service.
In previous releases of Volume Manager, the subdisk was restricted to
mapping directly to a VM disk. This allowed the subdisk to define a
contiguous extent of storage space backed by the public region of a VM
disk. When active, the VM disk is associated with an underlying physical
disk, this is how Volume Manager logical objects map to physical objects,
and stores data on stable storage.
The combination of a volume layout and the physical disks which provide
backing store, therefore determine the storage service available from a
given virtual device.