Serial Port Concentrators vs. KVMs
gary at umsl.edu
Wed Apr 23 14:23:19 EDT 2003
Having used both KVMs and serial port concentrators, I have my own
opinions about the advantages and disadvantes of each. I was hoping
that list members might share their opinions as well. My experience is
with Belkin 8-port KVMs and with a Computone RAS2000 serial port
concentrator. Here are some of my opinions, please feel free to add to
the list or correct me if I'm wrong. In particular, any comments on
scalability or some price comparisons would be interesting.
* Ease of Setup: usually you just run the keyboard/video/mouse cables to
the KVM and then a set of keyboard/video/mouse cables from the KVM to
some other node from which you can access the console for all of the
nodes attached to the KVM. There usually is nothing that needs to be
done with the OS (although I've heard of some BIOSes having problems but
I've never experienced this). There is also usually nothing to set up
with the KVM itself--just hook up the cables.
* Lots of cables: Even if you do not use a mouse cable, you still have
two cables running from the back of each node. I have heard of some
KVMs lately that use an adapter to combine all three kvm cables into
one. I have not actually seen or used one but that would certainly help.
* No remote access: The only KVM switches that I have seen with remote
access are "enterprise" KVM switches that have a high price tag. I have
no experience with this type of KVM switch but I would imagine it would
be like a hybrid KVM/serial port concentrator.
Serial Port Concentrator (SPC) Advantages
* Remote access: Most SPCs that I looked at listed remote access as a
feature. And some, including the Computone RAS2000 that I use, allow
you to access the them via ssh.
* Less cables: You only need to run one cable from the back of each node
(from the serial port) to the SPC.
* Multiple access methods: As noted above, you can access a lot of SPCs
via the network. But if that is down, you can also access the SPC via a
node that is attached via serial port to a special port on the SPC.
Serial Port Concentrator (SPC) Disadvantages
* Need to set up the SPC itself: In my case, this wasn't too bad.
Unfortunately, I would think that each vendor would have its own set of
procedures to follow for the setup of its own SPC.
* Somewhat of a learning curve: If you have not had experience with
serial ports (i.e., you know what they are but you've never done
anything with them), there will be a lot of terms that are unfamiliar.
You will also need to find out a lot of information about your hardware,
OS and BIOS. For instance, what speed do they support (9600 baud,
115200 baud, etc.)? What terminal emulation do they support (vt100,
vt102, ansi)? Is my serial port enabled in the BIOS? Which serial port
is which (For Linux: /dev/ttyS0, /dev/ttyS1, etc.)? And so on.
* A significant number of small changes to OS: There are a number of
changes that you need to make to the OS (in my case Linux) in order for
the console messages to be sent to the serial port. Thanks to various
how-tos and other docs, I was able to make all of the appropriate
changes but a lot of them were not very obvious (although once you read
about them you can see why it would be necessary).
* Must access the BIOS on each system: Unless your BIOS has serial port
redirection enabled by default (if it has this feature at all), you will
need to access each BIOS as you set the systems up (if you want to see
console messages generated by the BIOS).
Thanks for reading this somewhat lengthy e-mail. I would appreciate
gary at umsl.edu
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