Even if you're a medium-sized company with 500+ employees, there's still a good chance that most if not all of your servers live in a PC-style case, probably a tower, sitting either on the floor or in some form of rack.
Servers tailored for rack mounting on the other hand look quite different. Housed in neat metal cases, they slot directly into a rack shelf, which may well provide centralised services such as cooling and power as well as physical housing. A design originating from telephone companies, standard racks are 19 inches (482.6mm) wide with the height measured in units. You'll usually see this written as 1U or 2U, for example, with each unit being 1.75 inches (44.5mm). However, since rack servers tend to cost more, so why would you want to rack them up?
Business these days tends to be a round-the-clock activity but today's trend is towards specialised servers, one per application. So you might have one running the accounts database, one managing email, and another providing file and print services, plus various gateways and appliances for firewalling and traffic-shaping, for example. The upshot is that you're likely to have a fair number of servers running, and that means there's a number of good reasons to rack 'em up.
In this environment, it's much easier to provide physical security in a rack. You can lock them in and ensure that no-one can get at the systems to knock them over or accidentally hit the reset button.
In addition to keeping the machine safe from prying fingers, a rack enclosure can, if glass/perspex fronted, also help keep dust away from the servers, which helps lengthen component life, since dust-free chips run cooler.
Racks also offer easier cable management. Rather than the rat's nest that invariably develops when two or more cables get together, a degree of physical homogeneity means it's easier to bundle and label your cables.
Rack servers are more economical in their use of floor space so you can effectively stack half a dozen or more servers in the space where one or two used to live. In times of flat budgets but burgeoning demands for more server power, it can help you do more with less.
Most rack servers allow you to simply slide them out of the rack and either add or remove components, such as adaptors, CPUs or RAM modules, simply by lifting up a flap on the top. You don't have to unscrew a case and fiddle around inside the nightmare that the internals of a fully-packed machine tend to become. This can save a lot of hassle and time, making hardware upgrades much quicker -- less downtime should result.
As well as being easy to upgrade, rack-mounted servers are easy to replace with even denser servers incorporating blades, should circumstances require even higher density. Of course, there may well be other issues such as cooling that you will need to take into account but it's probably worthwhile having this argument in the bank, ready to be wheeled out when required.
Perception is all
It's also worth adding that a tidy rack full of servers, all blinking LEDs, will look much more impressive to the finance director than a jumble of assorted plastic beige boxes when he comes to see just where his money has gone.
Are there disadvantages? Depending on how mobile your business needs to be, racks take some dismantling which may be an issue. The upfront cost may be higher too, although this should be offset by the amount of time and money you save in the longer term.
Choosing and installing
Choosing the right rack will depend on the number of systems you intend to install -- or might possibly install -- and on the capabilities of cooling systems in the server room. If the air-conditioning is effective, you might be able to leave the rack open, while a warmish room might mean you need to install a dedicated cooling system for the rack enclosure.
You need to consider the weight as well as the size of the kit you're likely to install. Since almost all rack-mount servers are standardised at 19 inches wide, you should not find this a problem but it's worth checking. Check too whether your rack system includes power strips, and consider whether you want to install separate PSUs for each server. Place the heavy kit, such the UPS, at the bottom of the rack and don't forget to leave room behind the rack so you can easily manage the network and power cabling.
So, is it worth going for racks? Probably not if you're likely to move soon, but otherwise it could save you a lot of time and opens up the potential to move to blade servers at some point in the future.