Objective –

To Provide Information about populating a server rack / server cabinet, noting considerations to be taken into account while installing equipment.

Common placement of components will be noted, whilst discussing best practices for different setups and possible pitfalls.

Purpose

The purpose of this document is to assist and give understanding to those installing servers and placing other equipment into server racks & server cabinets, taking into consideration power requirements and mounting options, while noting reasons for doing so.

Scope

This document will cover areas including the physical set up of the actual server rack / server cabinet, the cat5 loom installation, power considerations, shelving, rack mount rails, shared racks, and security, with possible pitfalls to look out for.

Inclusions

This document includes information about common server racks & server cabinets setups, and different types of rack hardware.

Common practice for placement and installation of equipment is also discussed, while noting things to consider when purchasing server racks / server cabinets and equipment.

Exclusions

Due to the many different pieces of hardware and equipment available, this document does not cover information about every type of set up, or give a detailed step by step procedure on setting up server racks & server cabinets.

Physical Setup

Placement Of Components

Placement of components in a server rack / server cabinet depends on many different factors, the most obvious being personal preference. That being said there is still some common guidelines that should be taken into consideration when laying out a server rack / server cabinet.

The first step should always be the drawing up of a plan. This ensures that components are placed in the best position, maximizing space and ensuring that equipment is not needed to be moved halfway through installation.

When planning equipment placement, take into consideration existing equipment, possible future expansion needs, and the space gained from the removal of obsolete components.

Here are some simple guides when placing equipment:

• Put heavy servers and other heavy equipment (UPS) at the bottom of the server rack / server cabinet. This will save having to lift the servers too high. It will also help the stability of the rack ensuring that the rack does not become top heavy.
• Smaller servers should go above the heavy servers and equipment.
• Switches and purpose built firewalls should go towards the top of the server rack / server cabinet, possibly under the loom patches and a cable management tray (more on this later). There are a few reasons for this. Firstly, they are normally small and not too heavy, and secondly they are rarely needed to be taken out to work on.
• If monitors and keyboards need to be placed into the server rack / server cabinet, these should be placed at a height that is comfortable to use. If they are separate units, the screen can be mounted at eye height when standing, and the keyboard just above waist height. Combined units should be placed a little above elbow height to make the screen and keyboard easy to use.

Always ensure when lifting heaving equipment that there is someone available to assist, even if it is right at the bottom. It is always a good idea to have someone help with lifting and screwing in components that are above head height, even if they are light.

For ease of servicing and maintaining the servers, it is recommended that all components be labelled.

What To Put At The Back And Why

There are times when it makes sense to put equipment at the back of the server rack / server cabinet, but this will depend on what other equipment will be in the server rack & server cabinet.

Generally equipment that could be placed at the back of the rack could include the patch panel for cable looms, cable management tray for the loom patch panel, switches and firewalls.

These pieces of equipment are often not very deep and will fit at the back of the server rack / server cabinet at the top if there aren’t any deep servers that high up.

Why place these things at the back? Most servers have their network ports at the back as well as all the other cables. Therefore, if makes sense to put the switches at the back so that all the cables will be in one place and not running from the front of the server rack / server cabinet to the back. Also if the switch is placed at the back, then it makes sense to put the firewall and the patch panel for the loom at the back as well as these pieces of equipment that will be plugging into the switch/firewall.

Again the switches, firewalls, and patch panel for the loom should still be put at the top of the server rack & server cabinet as this is going to be the place with the most free space, and it will keep the server rack / server cabinet a bit neater, as well as the fact that these components will not need to be removed as often.

What To Put At The Front And Why

Most other components such as servers and KVM’s, monitors, keyboards, etc should be placed at the front.

These components should go at the front for easy access as servers will probably need to be moved out a few times, to upgrade ram or other components, during their life in the server rack / server cabinet. It also makes sense that if the servers are at the front of the server rack / server cabinet then the monitor and keyboard and KVM switches should be also.

Cable Management

Cable management trays should be installed with any loom patch panels that are installed into the server rack / server cabinet. This will help to keep the cables that run into the loom patch panel neat. It is also a good idea to install a second one with the switch if possible, to keep the switch cables neat and tidy.

Power

Considerations And Requirements

How much power a server rack / server cabinet will need depends on many different things. For one, it will depend on how many servers, switches and other components you will have in the server rack & server cabinet. It will also depend on how many PSU’s each of those pieces of equipment have, and also the power draw for each of the PSU’s that will be plugged in.

Some very general guidelines: each small switch would only take up 1 outlet, most servers would take up 2 outlets, (one for each PSU) and other equipment like firewalls and KVM’s would take up only one outlet.

Another consideration with power is to work out how much power draw all the equipment in the server rack / server cabinet will use and make sure that the power rails are going to be able to handle the load.

If there will be 2 power rails installed, then the rails should be plugged into different circuits. When setting up the equipment it is a good idea if a server or other equipment has 2 PSU’s, to plug each one of the PSU’s into a different power rail. This way if one of the power rails dies or something happens to the circuit that it is on, the other one should still be available.

Power rails, mounting, and different options

Vertical Mounting Rails

Vertical mounting rails are the preferred rails to use in server racks / server cabinets. The main reason for this is because they do not take up any rack units (RU’s) and they allow equipment higher up in the rack to be plugged into the higher points, keeping cable clutter to a minimum.

There are some draw backs to vertical rails though. The main one being that often they will be in the way of cable management trays on servers, and also they might prevent rapid rails and longer servers from fitting in the server rack / server cabinet correctly. They also make it hard to screw cage screws into the back rails.

These rails are generally mounted using the side cross braces that the vertical cage rails are screwed to. There are a number of mounting brackets that come with them so most of the time any drawbacks can be overcome by choosing the correct mounting bracket for the situation.

Horizontal Mounting

Horizontal mounting brackets are not used as much any more, but one place that they are good to use is in the shared racks or half racks. The reason for this is because they are small enough to fit in half, one third, or smaller parts of the rack, and therefore allowing each section of the server rack / server cabinet to have a dedicated power rail on its own circuit.

The main reason they are not used as much, and are not the preferred option for new installations is because they take up valuable rack space. People generally pay per RU, and they don’t want a power rail taking up RU’s that they are paying for. Granted that they can and are normally installed at the back of the server rack / server cabinet, but as the servers get deeper there is less and less space at the back of the racks for horizontal power rails.

The other downside to these horizontal mounted power rails is that there is only really one way to mount them. They do not come with different brackets for different mounting options, so you have to make do with what you have been given which makes it hard in some cases.

Shelves

Different Types Of Shelves

There are a few different types of shelves that can be used for different applications.

The 3 main types are:

• Light duty
• Heavy duty
• Counter Lever

Light Duty Shelves

These shelves have 4 points of contact with the server rack / server cabinet. 2 on the front rails and 2 on the back rails. They are only designed to support a little bit of weight, so it would not be advisable to use one of these shelves to support large servers.

A normal use for these shelves is to support small non rack mount routers and switches, and external drives. They are also sometimes used for light monitors and standard keyboards.

One of the things to note about this type of shelf is that because it requires contact with both the front rails and the back rails, it is necessary to make sure the shelf is long enough, or the front or back rails will need to be moved closer together to allow the shelf to sit right.

Heavy Duty Shelves

Heavy duty shelves are very similar to the light duty shelves. The heavy duty shelves require 4 points of contact, 2 at the front and 2 at the back. The main difference is that these shelves and mounting equipment are made to support a bit more of a load. It is still not recommended that multiple large serves be supported on one of these shelves even though they are stronger than the light duty shelves.

Normally these shelves are put at the bottom of the server rack / server cabinet to support tower servers that stand upright due to lack of mounting options on the tower servers, or simply because the servers are too tall to lay on their sides.

This type of shelf has the same consideration as the light duty shelf. It will need to be long enough to reach the front and back rails. If not, the rails will need to be moved to fit.

Counter Lever Shelves

Counter lever shelves are very different to the shelves mentioned above. The main difference is that they do not need to be the full length of the server rack / server cabinet to be mounted and able to hold equipment. They only need to have 2 points of contact, either on the front or the rear rails, depending on where you wish to put it.

These shelves are generally used to support light equipment like non rack mountable routers, external drives, or other type of light miscellaneous equipment.

These shelves only require 4 screws, 2 on either side of the shelf, and as has been said before, they do not need to be the full length of the rack to be mounted properly.

Why Use Shelves

Often there are times when shelves will need to be used. Not all equipment that you use will be rack mountable, this includes servers as well. Also often you will use a standard computer monitor and install it in your rack for use with your KVM switch.

In general, if a customer has something that they want in their rack, but it is not rack mountable, then this is the time that a shelf would be required. Make sure the shelf that is picked is the correct shelf for the situation, and the customer is aware of its limitations.

Rackmount Servers And Rails

Different Types Of Rails For Servers

There are many different types of rail setups for servers. Each server that comes with rails generally has its own type of rail. It should be noted that sometimes the same model server will have different types of rails.

Generally speaking, rails come in 2 parts. The part that connects to the server and the part that is installed in the rack. These 2 different parts are normally able to be separated, so that the rails can be screwed to the server and put them in the server rack / server cabinet, prior to the server being installed. There are also some newer rails that are one piece, these rails do not come apart, and normally you install the rails in the server rack / server cabinet, and then the server will clip into the rails.

Each different type of rail is installed in a different way. Some of them require screws to hold them in place, some of them will make use of the square holes and clip in place without screws, and some of them will clip in but require screws to keep them from falling out. If unsure how to mount the rails to the server or in the server rack / server cabinet, please refer to the instruction manual that are supplied with the rails.

Different Types Of Servers

There are 2 main types of servers. The first been being Rack Mountable servers, and the second being Non Rack Mountable servers.

Rack mountable servers are ones that screw into the racks, either using rails, or by some other means. These are by far the most common servers to find, as they are designed to fit in the racks, and make it easy to plan out and install servers and other equipment.

The non rack mountable servers are generally clone computers, or desktop machines that are being used as servers. This is not always the case, as there are non rack mountable servers, but a lot of the time you will find they aren’t really specifically designed to be a server. These types of servers usually need to be placed on a shelf. Depending on where the server will be positioned and what will be placed on top of it, and how it will sit , depends on which shelf to use.

Why Use Rails

If a server is supplied with rails it is normally best to use them. The main reason that servers are supplied with rails is to make it easy to pull them out and upgrade components. Using rails, the server can easily be slid out by 1 person and the new components installed and the server slid back into position, with no lifting needed. If the server did not use rails, then maybe another person will be needed to help lift the server down to the ground/staging area, and then install the components. Once all the components are installed, the server will have to be lifted back into the server rack / server cabinet.

If the rails that are supplied with the server are not used, then the server will need to sit on a shelf or on top of another server,

Why Use Server CM Trays

Server Cable Management (CM) trays are a great help for servers that are mounted with rails. If the server comes with a CM tray, then it should be used if there is room at the back of the server rack / server cabinet. The CM trays that come with servers generally attach to the back of the server, and the back mounting rail of the rack. When the server is slid out it expands, and when the server is pushed back in the tray folds up again. Inside the tray are all the cables that are connected to the back of the server. Often this is only a network cable and a power cable (maybe 2), but if using KVM’s or have external SCSI backup drives, then there will be more cables.

The main purpose of the tray is to keep the cables neat and to make it easy for the server to slide out on the rails without letting the cables get tangled or caught on the servers below it. It also helps keep the back of the server rack / server cabinet neater because the length of cables are now in the cable tray instead of just hanging from the back of the server.

Shared Racks

What To Do About Server Rack / Server Cabinet Layout

When sharing a rack between more than one person, the rack should be divided into sections for each person. The different people’s equipment should never be mixed up. The rack layout for each person in the shared rack should follow the guide lines above, but remembering that the top of the rack for each one of you, is now the top of your section. Generally speaking if you are sharing a rack with others you will not have a lot of equipment and probably wont have KVM’s or monitors.

When deciding where to put a someone in a shared rack (Top, Bottom, Middle, etc) take into consideration what type of equipment the they will have, will they have a couple of 4RU servers? Put them at the bottom or as close to the bottom of the rack as possible. Will they have lots of little 1RU servers? Put them at the top or in the middle of the shared rack. If they are likely to expand and eventually want more rack space, assign them a section of a rack that is not used much or at all, and then in the future you have the option of giving them the rest of the rack without having to move them.

Separation Of Server Rack / Server Cabinet Areas

The easiest way to visually separate different people in the same rack is to use a shelf. This gives each person a base to start with and also shows the person below them where their section ends and how much room they have left.

Doors

Types Of Doors And When To Use Them

There are a few types of doors that can be put on the server racks / server cabinets. Most of the racks will have doors that are made of some type of metal, and have lots of little holes drilled in them. These are the doors that should be used when the equipment inside needs to draw air in the front and blow it out the back. This is nearly all equipment in the data center. If a server rack / server cabinet has a few servers in it, or a few big switches then this is the type of door that should be used.

If the rack is only there to house cables or a small switch or a backup drive, or some type of equipment that does not need a lot of airflow, then a Glass door on the front may be used. It is always a good idea to have a vented door on the back of any rack, because nearly all equipment will blow air out the back. This also means that there is always somewhere for the air to escape and enter if using a glass door on the front.

One advantage of glass doors is that the equipment inside can be seen and see if it is running without needing to open the door. This can also be a disadvantage as it means that everyone else can see what is inside the rack.

Generally speaking, some form of vented metal door should always be used and glass doors should not be used unless nothing else is around, and you are sure that the equipment inside the racks will get enough air flow.

Things To Look Out For

As with everything there are always things that are overlooked when planing and testing. Here are a few simple things that should be taken into consideration while planing the rack and setting everything up.

First thing to remember is to check that the server rack / server cabinet will be deep enough to fit the equipment purchased. There is nothing worse then having a 900 or 1000 deep server and finding out that the rack is only 800 deep.

Make sure that the possibility of expansion is taken into consideration. Try to determine if you are going to require more rack space in the future, and if so try to position equipment in a location that will enable you to expand without trouble, or downtime.

Make sure that there will be enough power points for the equipment that you plan to use. More and more people are using 1RU servers, which means that they can fit a lot more of them into their racks. The more servers in the server rack / server cabinet means the more power points they are going to use.

Keep the cables tied together and out of the way of things, use the cable management trays if they came with servers, and for networking, use the cable management trays provided. The neater the cables are the easier it is to work on the servers and add more equipment.

Make sure that the type of mounting rails in the rack will work for the rail system of any of the servers that will be installed. If the rails have each RU as a series of Square, Round and Square holes, this will not work for all types of server rail systems. You might need to replace the mounting brackets with ones that have a Square, Square, Square hole system.

References

(1) “Rack Layout”. Retrieved from: http://www.hurgh.org/articles.php?article=rack_layout