Storage Area Networks For Dummies®

Chapter 5: Designing the SAN
137
available, because the vendors fix bugs in the drivers and add new functionality
that you might be able to take advantage of. (For more about HBAs and
their drivers, see Chapters 1 and 2.)
Use unique zone alias names
If you’re setting up a SAN with two fabrics, such as Fabric A and Fabric B,
make sure that all your zone information is unique between the two fabrics.
We mention this because if you ever have to connect the two fabrics together
for some reason, you’ll have problems if the non-unique information is contained
in both fabrics.
Take the domain ID of the switches, for example. Because you have two
fabrics, you can use the same IDs in both fabrics. You might have two ID 1s,
two ID 2s, and so on. If you try to connect the fabrics together under those
circumstances, the switches will reject the connection if they find the same
domain ID in both fabrics.
Using storage from multiple vendors
When using storage arrays from multiple storage vendors in the same fabric,
use zoning to put them into separate zones. This keeps them as separate
management entities; also, if one vendor’s array has some weirdness going
on with it, it won’t affect the other storage. If you also use single-server zones
that include only a storage port and a single server, it will keep your SAN running
smoothly when devices are added or removed from the fabric.
Always use two fabrics
When you use two SAN fabrics instead of one, your SAN can withstand failures
of any device in a single path. You can lose a cable, HBA, switch, or
storage port and still have your applications available. Using two fabrics
also enables you to do normal maintenance to the SAN without any planned
downtime, because you can maintain one fabric at a time. Using two fabrics
does require twice as many HBAs (two in each server, plus fail-over software)
and twice as many switches — but these are worth it in the long run. This is
especially true if downtime is costly to your business.