Storage Area Networks For Dummies®

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Part IV: SAN Management and Troubleshooting
reference to see whether it could be related to your current issue. The log is
either in the memory of the SAN switch itself or on a management console
that monitors switches for these types of events.
Broken fabric switch
Here, I’m talking about a switch that’s physically broken, not a software corruption
or configuration that went astray. (I cover those situations in the
upcoming section “Continuous problems.”)
A good SAN switch has many redundant features, such as dual power supplies
and multiple fans. Most switches have a network connection to send
Simple Network Management Protocol (SNMP) alerts to your SAN management
framework server that monitors the whole SAN. A catastrophic outright
failure of an entire switch is unheard of (knock on wood), but it is possible.
Your SAN management framework should be able to alert you about powersupply
failures, fan problems, ports going bad, or even an outright disappearance
of your SAN switch from the rest of the fabric.
The most important thing is that you have a backup of your switch configuration
somewhere. If a switch is toast and needs to be replaced, would you
know the zoning and port configuration off the top of your head? Didn’t think
so. For this reason, it’s important to have this configuration saved somewhere
off the switch itself.
In a single-switch SAN, or one with two switches that aren’t directly connected,
the configuration of the SAN is isolated to that switch. In other words,
all the settings that define what port can see what other port (zoning) and
how those ports are supposed to communicate (fabric, point-to-point, loop
mode, and so on) are all self-contained on that switch only. If you had to
replace that switch with one fresh out of a box, you’d have to replace the configuration
manually.
Most switch vendors have a command that you can issue to the switch to
make it save its current configuration to a file somewhere on your network.
The process usually requires a protocol such as File Transfer Protocol (FTP)
to log in to a server on your network and save a file that contains all the
zoning and switch parameters. Then this file can be restored via a command
to the switch at any time (usually, if something goes horribly wrong).
Figure 12-2 shows the two directions that a configuration can go in: dumped to
a server for safekeeping or loaded back to a switch to restore a configuration.
In multiple-switch SAN fabrics, the switches share the configuration information,
so if you plug a brand-new switch into an existing fabric, it learns the SAN
configuration from the other switches. Check with your switch vendor, but
most switch manufacturers are adopting this automatic configure process to
make adding onto or replacing switches easier.