Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Figure 1-3
Example configuration for disk enclosures connected via a fibre
channel switch
enc0 enc2
Host
Fibre Channel
switch
Disk enclosures
c1
enc1
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.
In most disk arrays, you can use hardware-based storage management to represent
several physical disks as one LUN 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 disk or a LUN.
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 configured only on the disks in enclosure
enc1, the failure of the cable between the switch and the enclosure would make
the entire volume unavailable.
If required, you can replace the default name that VxVM assigns to an enclosure
with one that is more meaningful to your configuration.
See “Renaming an enclosure” on page 189.
25Understanding Veritas Volume Manager
How VxVM handles storage management