Storage Area Networks For Dummies®

Chapter 5: Designing the SAN
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WWN zoning (soft zoning) is more flexible than port zoning (hard zoning)
because the zone information is based on the device’s address instead of
the port on the switch that it’s connected to. If a switch port goes bad and
you move the device connected to that port to a different port, you need to
change the zone information to reflect the changed port before the device connected
to the new port will work again in the fabric. By using WWN zoning, the
address will have moved with the device, so no zone changes are needed.
Hard zoning
Hard zoning is a method of grouping individual physical switch ports in
a switched fabric together into a zone that only allows communication
between physical ports on the switches. (See Figure 5-31.) Only the physical
ports in the zone can communicate with each other. No other ports in
the fabric can communicate with those ports, and members of that zone set
cannot communicate with any other ports in the fabric.
Zone members can communicate only with other members of their zone. A
zone set can accommodate multiple zones; switch ports can be members of
multiple zone sets. If a switch port is made a member of multiple zone sets, it
can communicate with the ports of all the zone sets that it has membership
with. The same holds true for soft zone members (see the preceding section).
Hard zoning at the level of physical ports is the most secure method of zoning.
You can mix domain and port names along with WWNs in the same zone, but
after you do, all the ports revert to soft zoning. (See Figure 5-32.)
Zone alias names
An alias is a custom name that you can assign to switch ports and WWN
addresses in a zone. You use an alias to rename the port names of the switch
and the WWNs of the HBAs connected to the switches with something that
makes more sense to a human. Trying to figure out what has access to what
by using port IDs and/or WWN addresses is hard. Using more human-understandable
naming makes better practical sense.
As an example, suppose you have four servers and one storage array in your
SAN, as in Figure 5-33. This is your production SAN. Two of the servers run an
Oracle database under Unix, and the other two run your mail system under
Windows NT. The servers each have two HBAs apiece, connected to the storage
array through two different switches. As you can see from the figure, the
switch ports assume the address of the HBA of the server that’s plugged into it.