VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
How VxVM Handles Storage Management
Chapter 18
In a typical SAN environment, host controllers are connected to multiple
enclosures in a daisy chain or through a Fibre Channel hub or fabric
switch as illustrated inFigure 1-3
Figure 1-3 Example Configuration for Disk Enclosures Connected via a
Fibre Channel Hub/Switch
In such a configuration, enclosure-based naming can be used to refer to
each disk within an enclosure. For example, the device names for the
disks in enclosure enc0 are named enc0_0, enc0_1, and so on. The main
benefit of this scheme is that it allows you to quickly determine where a
disk is physically located in a large SAN configuration.
NOTE In many advanced disk arrays, you can use hardware-based storage
management to represent several physical disks as one logical disk
device to the operating system. In such cases, VxVM also sees a single
logical disk device rather than its component disks. For this reason,
when reference is made to a disk within an enclosure, this disk may be
either a physical or a logical device.
Another important benefit of enclosure-based naming is that it enables
VxVM to avoid placing redundant copies of data in the same enclosure.
This is a good thing to avoid as each enclosure can be considered to be a
separate fault domain. For example, if a mirrored volume were
c1
Host
Fibre Channel
Hub/Switch
Disk Enclosures
enc0 enc1 enc2