VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Device Discovery
6 VERITAS Volume Manager Administrator’s Guide
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 manyadvanceddiskarrays, youcan usehardware-basedstoragemanagement to
represent several physical disks as one logical disk device to the operating system.
In suchcases, VxVM also seesa single logicaldisk device rather than itscomponent
disks. For thisreason,when referenceis made toa disk withinan 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 enclosurecan beconsidered 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 hub 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 102
for details.
In High Availability (HA) configurations, redundant-loop access to storage can be
implemented by connecting independent controllers on the host to separate hubs with
independent paths to the enclosures as shown in “Example HA Configuration Using
Multiple Hubs/Switches to Provide Redundant-Loop Access.” Such a configuration
protects against the failure of one of the host controllers (c1 and c2), or of the cable
between the host and one of the hubs. In this example, each disk is known by the same
c1
Host
Fibre Channel
Hub/Switch
Disk Enclosures
enc0 enc1 enc2