After Hours

10 things to look for in a KVM switch

KVM switches can make your life infinitely easier -- unless they don't support the features you need in your environment. Erik Eckel offers some suggestions for making sure you don't wind up with the wrong KVM for the job.

IT professionals spending any significant time in server rooms know the importance of good quality keyboard/video/mouse switches. Plagued with a poor performing KVM switch, even mundane tasks -- such as cleanly rebooting systems, confirming successful backup operations, downloading and installing OS updates, and completing general troubleshooting routines -- become needlessly complicated.

Whenever you buy a new KVM switch, you want to make sure it meets your requirements. Review this list to avoid common errors many rookies or budget-minded organizations suffer when selecting a unit too quickly or without performing the necessary homework.

Note: This article is also available as a PDF download.

1: Proper operation

Little in IT is as frustrating as not being able to properly view a critical system or connect using a standard keyboard or mouse, especially as the issue seems to arise at the most crucial times (an email server is down, the Internet has failed, hundreds of users are affected, etc.). When you're combating a stressful failure or outage, that's no time to have to fumble around with a flaky KVM.

Perform some due diligence. Whenever you think you've found the perfect KVM, search Internet forums and read Amazon, Newegg, and other reviews to learn what others' experiences have been using the same model. If feedback is positive, you're good to go. But if proper operation in the real world proves troublesome, keep searching.

2: Compatibility

KVMs often work with most operating systems, but occasionally glitches arise. Review a model's specifications to make sure it's compatible with the operating systems it must support. If you don't, you'll have to box everything back up, request an RMA, and send it back.

3: Required connections

I've seen seasoned engineers purchase new KVMs that support only DVI video connections or only PS/2 peripherals, then discover the servers all have USB- or VGA-only connections. In other cases, engineers assume that the model they're buying provides KVM over IP support, when it doesn't.

Don't order a KVM switch haphazardly. Confirm that models support the connections in place, which may require a quick-and-dirty audit of current equipment prior to ordering, especially when equipment from multiple locations is being combined in a single site for the first time.

4: Port expansion

Shortsighted administrators often purchase eight-port KVM switches when they need to support eight servers. Whenever possible, purchase KVM switches with additional capacity. Unforeseen but reasonable decisions to add a VOIP system, new database platform, HVAC- or alarm-controlling servers, and other devices instantly place you at a deficit. Too often, organizations end up with more systems than ports; if possible, purchase KVM switches with 20% to 25% extra ports.

5: Onscreen display

Onscreen displays (OSD) and menus are kind of like rear-window defrosters -- you don't miss them until you don't have them. They provide visual indications of which systems are online or connected, making it easier to configure settings and switch between systems. If you're accustomed to working with GUI assistance, select a model that supports OSD. Also consider OSD-enabled KVM switches if you have to switch frequently between numerous systems, as OSD will make you more efficient.

6: Mount options

Desktop KVMs work well within many organizations, but they don't work well when migrated to server racks. In businesses experiencing growth but working without a current server room or even half-rack, look for KVM switches that can be converted to rack mount, should the need arise. Or start with a standard rack mount unit. Select desktop models only if you're confident the unit will never end up servicing systems mounted in a professional rack or cabinet.

7: Electrical power

KVM switches with their own power supply work more consistently, in my experience, than do those that draw their electrical supply from the systems they connect to. Even many budget-priced KVM switches include optional power supply connections but don't ship with a standalone power adapter. Always check to see whether a power adapter is included with, or supported by, the unit you select. If no power supply is included, visit a nearby Radio Shack or electronics store to purchase the missing component, after assuring its compatibility.

8: Sufficient cable length

More than once, I've seen six-foot KVM cables prove too short when wound through cable management infrastructure. As part of a pre-purchase audit, measure the distances the KVM's cables must cover. Ensure that included cables, or those you purchase separately, are long enough to span the required distances. It sounds academic, but KVM cables are expensive, even when purchased in bulk, and they are painful to have to rerun in server cabinets after discovering the just-purchased items are too short.

9: Reset button

Occasionally, KVM memory becomes corrupted. Since KVMs frequently receive power not only from a standalone power adapter but also from the systems the KVM switch is connected to, it can prove difficult to clear a corrupted KVM switch's electronics. No one should have to climb behind a server rack to physically disconnect four, eight, or even 16 systems just to clear a frozen KVM. Look for systems that have a simple reset button.

10: Audio support

While less common, some environments require that system audio be available from the systems the KVM controls. Of course, not all KVM switches support audio. Review a specific model's individual specifications to confirm that it will support audio. Otherwise, you could find yourself stuck with convoluted workarounds resulting in a cacophony of noise. Prevent headaches. KVM switches can be very unforgiving. Perform your homework up front.

About

Erik Eckel owns and operates two technology companies. As a managing partner with Louisville Geek, he works daily as an IT consultant to assist small businesses in overcoming technology challenges and maximizing IT investments. He is also president o...

11 comments
Micheljordon
Micheljordon

I guess you've covered all the points to check before buying KVM (Keyboard,Video,Mouse) switch

these will prevent from headaches of users!

SamFrench
SamFrench

1) For each server: Create a high contrast, 1024 x 768 graphic with that server's name, box function(s) and IP address(es) centered. Place those on each server's desktop, as it's wallpaper. That way, your KVM display will always accurately reflect the name of the machine your K, V and M are truly addressing. I use bitmaps (named "thisbox.bmp") that can be effortlessly edited using MS-PAINT (in place, on the server itself) and, though I'm no fan of a cluttered C: root drive, using that location as a server room standard to store each box's particular graphic keeps the editing process simple and stupid. 2) As a backup, I keep a soft-copy simple table, numbered 1-x where x is the last KVM port number, populated with the current box names, functions and IP addresses assigned to KVM switches on my laptop. I print out a new copy after making any changes and put that under the keyboard of each KVM switch. In a worst case scenario with several boxes down, this will tell you which two boxes aren't working faster than anything else. If this is maintained as an ASCII text document, at least one thing will go right in a TRUE worst case scenario. 3) OSD's are a great idea but the more you depend on them, the longer your requirements list for them becomes. And, seriously, how easy is it to forget the uber-quirky keystroke combo you must perform to get into the display name editing mode? ("Was it Ctrl + Alt + LeftShift + F9 or...?") As the feature you use the least, once you're all set up and ready to go, it's the most likely to be forgotten. Moving two boxes around, adding another box to the rack, renaming a box... any of these tasks can render the stored box name data totally useless. It's never long before one, two, six (or more?) switch numbers are mis-labeled making ALL the display names unreliable. Clearing them, of course, is simply a matter of the KVM control box losing power which happens frequently enough to make even the most conscientious server Nazi drop his OSD use. 4) I love KVM's that use male ports on the back of the acutal switch! All you need for cables are standard extension cords which are a lot cheaper, exponentially more available (You can buy them at Wal-Mart, Radio Shack, Best Buy, Office Depot... I've even seen them at Albertson's!) And they come in more lengths than most of the male-male proprietary patch cords you have to buy with many KVM offerings. Resist the temptation to patch two six foot cords together in order to cover 10-12 feet. Spring for a 12 foot cord! (Patches-BAD) 5) If you end up selecting an expensive KVM with 16 ports, you're a fool if you don't buy 16 sets of the longest cables that manufacturer sells. You're also foolish NOT to confirm that any proprietary cables required are at least standardized across that manufacturer's line of KVM's. Yes, cables can be expensive but, as KVM components go, they're the most reliable element of any KVM set-up. You'll have a full set of 16 cables lying around for much longer than any other KVM purchases. 6) Before you cable ANYTHING, do yourself a favor and label both ends of every cord (or group of cords) with port numbers corresponding to the KVM hub port numbers you'll be patching to. To be clear: If your KVM hub has 16 ports, you should have sixteen (sets of) cables, individually labeled at BOTH ENDS with numbers 1-16. Manually tracing cables to/from the hub and the boxes they're connected to is a B*TCH. Also, once populated, KVM port labels can become difficult to read. If, however, you can read the end labels of the cables to each side of a vacant port, it's easy to ascertain the empty port's identity. 7) Before you cable ANYTHING, do yourself another favor: Buy a couple bottles of inexpensive white or yellow nail polish. Swipe the top ("flat") side (or what should be the flat side) of all PS-2 cables. The flat side is the one opposite the two pins sitting close together. (see below) TOP

Spncr592
Spncr592

Regarding OSD, the on-screen display can be extremely useful for KVMs installed in a rack, particularly 8 or 16-port varieties, however for a 2-port or 4-port desktop KVM it's typically not as important since most people can without much effort keep track of what computer is on what port. Also, something to note is that Windows 7 has a tendency to create huge headache problems with many KVM switches due to the way it frequently polls the display to check on what display is connected and what resolutions are supported. For that reason you'll want to make sure your switch provides a dedicated active DDC/EDID channel to all ports so Windows will always be able to see what display is connected, regardless of what port you're on - that way you can avoid the no-video or desktop resizing issues frequently seen with Windows 7 and KVM switches. Otherwise you can get an EDID emulator that will sort of patch the problem for that one system. And yeah, non-proprietary cables are ideal so you can use separate VGA (or DVI) and USB cables for custom lengths, if needed - without having to pay nearly $50 to get them from the KVM manufacturer.

CorporateLackie
CorporateLackie

Note also the maximum resolution the KVM supports...

apotheon
apotheon

If you're using racks of servers, you may want to bypass a KVM switch entirely and go with a serial console server. If you're looking for a desktop KVM switch, though, there's another problem that might arise: how well it handles inputs from the specific keyboard and mouse devices you use. One particular area of concern I have encountered is the case of a mouse and keyboard that come with a single USB dongle for a wireless connection. Some KVM switches -- even those that claim to be able to support that setup -- will work unacceptably badly, such as failing to pass certain keypress events through, unusable levels of lag for mouse events, and so on. Unfortunately, I have not found any solution to this problem other than trial and error.

TBone2k
TBone2k

A few times it would have been handy when at a client site if I could have used my laptop as a KVM. Remote desktop is all well and good, but not so great when the system won't start. Plus a lot of small operations don't want to leave a monitor hooked to a server all the time.

CharlieSpencer
CharlieSpencer

I use a KVM on my work bench to manage whatever client devices I'm working on. A KVM with an integrated hub means one less box on my bench.

TBone2k
TBone2k

Especially if you are buying a larger KVM than you need at the moment (point #4). Some manufacturer require that you buy their special cables. Although proprietary cables generally cut down on clutter in the rack, I found they can be expensive or hard to find, especially if you have to buy more after the fact.

speckmc
speckmc

so just purchase with all the cables, that way when you roll in a new system, you don't have that "oh crap I forgot to order an extra cable" moment..

TBone2k
TBone2k

You are right, but proprietary cables are also expensive. And if you work in an environment where you have to keep costs down, sometimes you can't buy all the cables at once. However, its a good idea to see if the manufacturer has a "package deal" that includes all the cables. That gives you everything as a single line item that is harder to be trimmed.

speckmc
speckmc

I've found that i have to purchase things from multiple vendors at times to get what i want for the prices i want.. might take a few minutes longer but if you purchase the kvm from one place, and they don't have a package deal, chances are you can find the cables cheaper through one of your regular vendors..