Chapter 1: Cabling Concepts and Best Practices 9
How Initiators and
Targets Respond to
Zoning
When an initiator first accesses the fabric, it queries the World Wide Identifier
(WWID) name server for all of the attached disks and drive trays and their
capabilities. Zoning is like a filter that the WWID name server applies to the query
from the initiator that limits the information returned by the WWID name server to
the initiator. A zone defines the WWID of the initiator and the WWID of the devices
that a particular zone is allowed to access. Devices that are not part of the zone are not
returned as accessible devices.
The fabric provides universal access for all initiators and targets. Any initiator can
query (probe) the fabric for all targets, which can affect performance when many
targets are connected to the fabric. The querying process also provides access to
devices for which access is not needed. Use zoning to limit the number of devices that
an initiator can access. Within your storage area network, you should zone the fabric
switches so that the initiators do not “see” or communicate with each other.
How Best to Approach
Zone Configuration
Some of the cabling topologies shown in this document require the use of a zoned
switch. By default, the switch uses no zoning, which is not sufficiently robust for
most applications. You must configure the switch before you use it.
Zone configuration is managed on a per-fabric basis. While you can administer zone
configuration from any switch, use the best practice of selecting one switch for all
zone administration. Give preference to the primary switches within the SAN, and
choose only a switch that has the most up-to-date storage management software and
switch management software installed on it.
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