[LUNI] How to get many serial ports cheaply

[bradbosch at attbi.com]

Carey Tyler Schug writes:
 > I have a bunch of unix computers that I run from a serial interface, and 
 > now am adding cisco routers that also are controlled by serial 
 > interfaces.  Other then a plethora of cascaded RS-232 switch boxes, what 
 > are my options?

In our firmware development lab where we currently have about 20
serial devices to support, I've been using cheap USB RS232 serial
adapters which Frys recently frequently has on sale for $15 each.  I
combine these with a $4 unpowered 4 port USB 1.1 hub (also frequently
on sale at Frys) for up to 16-24 ports/Linux lab support host.
Combining this with conserver ( http://www.conserver.com ) allows
transparently distributing the serial ports over multiple Unix or
Linux console servers with convenient authenticated access from the
network by port names you choose.  Conserver also provides a way to
see who is using a port and for multiple users to access a port.

You can also transparently mix existing serial tty ports with the USB
adapters using conserver.

The USB cables on these adapters tend to be short, so depending on how
close together your RS232 devices are, you may need to buy hubs with
long cables or buy some USB extension cables or buy DB9 extension
cables.

The trick to using conserver with the USB adapters is figure out the
USB discovery order by plugging them all in first and then reboot the
server or reload the USB modules.  After this, you can label each port
by individually unplugging and re-attaching each device while
monitoring kernel messages to determine which port number each adapter
has been assigned.  This way the ports will all be assigned the same
numbers the next time you boot.  Once you know the discovery order of
your USB ports and hubs, you can add more adapters (in order) without
rebooting.

Since we needed the Linux servers for other things anyway, our
cost/port is about $16.  There may be cheaper solutions, but this one
is quite flexible and works well for us.  Using larger hubs or
multiple conserver hosts, this should easily scale to several dozen
console ports or more.

--Brad