KVM (Keyboard Video Mouse) Switches – What to Look for
The KVM “console” itself is just the keyboard, display, and pointing device mounted into a single rack-mountable unit. The KVM "switch" is what allows you to connect multiple servers to one set of keyboard, display, and pointing device. So you need the KVM console and switch together along with adapters to connect the servers to the KVM switch. When pricing out a KVM setup, make sure you know who much each adapter costs because it will add up as you add more servers to the switch.
When comparing KVM consoles, check the keyboard keys to see if they are standard. I’ve seen one one keyboard that had the DEL key in a non-standard position which made pressing CTRL+ALT+DEL an annoyance.
Newer KVMs use standard Cat 5 cables to connect the adapters to the KVM switch. The adapters have RJ-45 ports on one end and USB/PS2 and VGA ports on the other end. This takes away the clutter with traditional KVM cables that were very bulky. Note that the Cat 5 cable does not go through a regular network switch or hub or anything of that sort; it goes directly from the adapter to the KVM switch. Cat 5 cable is only used as a connection medium because it’s common and readily available.
Some KVMs, such as the Avocent AutoView 3200, allow cascading of KVMs so that you can have one “master” KVM and several “slave” KVMs attached to it. So if you had a 16 port switch and needed more ports, you could cascade another 16 port switch off of the master for an additional 16 ports. Note that one port on the master switch would be used by a KVM module to connect to the analog console KVM ports of the slave switch, so you would end up with only 15 usable ports on the master switch.
What is network-related is the KVM-over-IP technology (aka IP KVM). KVM-over-IP switches allow you to connect to them via IP address over the regular network and control any device that is connected to them on the analog side. Some switches are referred to as analog or digital, or both. The digital part is the network connection on the switch that administrators connect to via TCP/IP. The analog part is the connection from the KVM switch to the server and the ports on the switch that allow you to connect a KVM console directly to the switch. Analog KVM consoles are the old style KVM consoles where you'd have to be standing in the server room working directly on the KVM console. KVM-over-IP allows you to connect to the analog KVM console from across the network.
To make it cross-platform and easy to use, you typically connect to a KVM-over-IP switch using a Java-enabled browser. The session would be encrypted and require a user name and password. After you connect, you’d be able to access any server connected to the switch on the analog side. So it’s not a bad way to get console-level remote control of your servers. You’d just need to connect to the switch IP address instead of connecting to each separate server with tools like DameWare or DRAC (Dell Remote Access Card).
Some more advanced features allow remote power cycling and virtual media access (just like with a Dell DRAC card and the like). The big downside with KVM over IP is that since it uses the network infrastructure, if your network is down, you’ll need to walk over to the console. Some switches do offer a serial connection for an external modem for fault tolerance.
The Avocent AutoView 3200 allows you to assign a name to a module so that when you view the switch menu, you’ll see the name assigned to the module regardless of which port you plugged the module into. This is a nice feature if you ever have to move your servers around. This feature is possible because each module has a unique ID.
Note that Avocent actually manufactures KVM switches for Dell, HP, IBM, and others. I don’t know if those companies add any value to the product other than rebranding it. But it’s possible that their KVMs might have additional features that work better with their servers. If you just need basic KVM features, then you can go with Avocent directly (From my one experience with Avocent, I feel that their documentation and support are subpar--see my post about this).
ADDITIONAL RESOURCES
http://www.dell.com/content/topics/global.aspx/power/en/ps3q02_avocent?c=us&cs=555&l=en&s=biz
http://www.dell.com/content/products/productdetails.aspx/pedge_2161ds?c=us&cs=04&l=en&s=bsd
