The Bottom Line Rack mounted configurations have a variety of positives and negatives which must be addressed with careful planning.

Here at Manugistics headquarters in Rockville, MD, we currently are running an enterprise datacenter in which we have about 15 or 16 racks full of nothing but Dell and Digital servers. We have then another 2 or 3 which are composed of enterprise Sun components running Solaris platforms for various uses.

Before the big internet explosion, there was two options for medium to large companies in terms of setting up a data center for sharing and processing. You could either buy large mainframe computer from one of several large companies (IBM, Sun, HP, Digital), and then line them up in a row and set up enterprise UPS protection and data center climate control, or you could buy a number of less powerful computers and set them up in a distributed manner throughout your comapny, usually placing the various "servers" geographically close to the area that will use them most.

The problems with these early options are obvious: You had to choose to either spend huge amounts of money to buy or lease large servers or you had to face an administration nightmare. Many companies did not have the resources to get ahold of some of the larger server equipment and thus would be forced to set up administrative nightmares of a data center: buying workstations on shelves to act as servers, placing them in closets and hiding them whereever they could.

Now, with the aid of rack mounting technology support by major vendors, coupled with the ease of logical network monitoring in domain and workgroup environments, we no long have to deal with these sort of problems as we now have the ability to use rack mounted servers.

A rack itself is a metal frame (usually armor-grade steel or hardened aluminum) that stands about 6 feet tall, nearly (but not quite) two feet wide, and anywhere from 6" to 3 feet deep (depending on the application). Rather than having solid faces, the rack will either be built (in the case of thin racks) to cantilever servers, hubs, switches, or other network peripherals or (in the case of full-frame racks), can be built with front and back facet holes to allow rackmount trays and slides to securely hold weighty servers in a strong and stable environment. The rack mounted servers themselves do not usually attach directly to the rack but rather get mounted on to sliding trays or slides which are in turn mounted to the rack.

In the case of rack-mounted Sun servers, when a company leases them (they are almost always leased, never bought as a single server can cost upwards of $50K-$100K), they are usually shipped on a palette, already rack mounted except for any additional peripherals that the company leasing them has ordered. Just recently, we ordered a Sun Sunfire server that came in such a configuration and we had to rack mount two of the boot devices. Sun usually custom builds different racks for different servers, complete with cable management solutions pre-built into the frame.

Dell servers, on the other hand, are not usually sent each with a special rack. Dell builds a number of differnt sizes of racks that employ a more or less modular approach. In essence, they want you to be able to mount just about any Poweredge server in the same rack as any other poweredge server. This means that a Dell poweredge 1550 can be mounted in 1U on the same rack as a Poweredge 6400 is mounted in 3U. So any model they make can be mounted on the same sort of rack which reduces interchangeablility problems and allows enterprise companies to use the same racks for different hardware.

Rack mounting equipment is not all fun and games, however. Unfortunately, rack mounting servers has some real limitations that can damage your equipment if you do not observe and protect against thier impact. Computers use electrical signals running at high speeds through circuits, switches, and boards as they pass on thier data trip. A computer functions by using resistance to block or unblock passages for that electrical charge. Because of the resistance that is happening in billions of places in the many parts of a server, a significant amount of heat is generated, and a rack mounted server is no exception. With rack mounted servers, you are further complicating the problem by putting large numbers of these computers in a densely populated environment causing a damaging envelope of heat if not properly cooled.

Another historical problem with rack mounted servers is the huge number of cords that will have to be dealt with. For each server (using the dell poweredge 6400 in this example, with the configuration we most commonly use) that we mount in a rack, we have 4 cat5 ethernet cables, 3 power cables (there are three power supplies on a 6400 in order to provide redundant power fault tolerance), A monitor/mouse/keyboard cable that runs to our KBM enterprise equipment all mounted on to a flimsy cable arm and then routed to the various places the cables have to go. If you place 6 of these servers on the same rack, you have just condensed together 24 cat5 ethernet cables, 18 power cables, 6 KBM cables, and 6 metal arms, thus creating a rack mounted cable nightmare and thats just for one rack! Imagine working in a data center where 3 or more can be side by side all feeding in to similar areas.

While there are solutions for each of the above problems, they require planning beforehand, extensive and complete. It is the job of the systems administrator to make sure that each of these problems are properly addressed and that each has been taken care of. Perhaps in the future, looking at blade-mounted configurations, we will be able to condense some of these problems and alieviate them completely. For the present, however, we simply hav eto allow and plan for them.

Rack mounted configurations have a wide variety of positives and negaives which must be individually weighed before implementing a solution. It requires careful planning and a significant level of ability to execute a proper implementation. Hopefully in the future some issues can be addressed with blade mount configurations but for now, all we can do is work with what we have.