# The Design and Organization of Data Centers/Racks and Cabinets
## Rack-mount systems in general

The quality and layout of your racks and cabinets can save you hours in frustration, keep your equipment organized, and reduce the length of downtime by speeding repairs.
When comparing racks and cabinets, examine the items in person. Ask to see some in a data center near you. Buyer beware.
Vertical columns with holes for mounting equipment
Over the years several different rack mounting scemes have come out, varying from 16" to 49". These widths are measured horizontally from centre of hole to center of hole.
The 2 surviving standards are the 19" and the 23". The 23" standard is used by the telecommunications industry and virtually everyone else uses the 19" standard.
Equipment intended for rackmount is sized vertically by "U" units, which equals 1.75 inches.
Compliant hardware is built in multiples of this 1.75" unit.
There were tape measures made that were calibrated in rack units, they are difficult to find.
Note that the holes are unevenly spaced. Narrow gap, wide gap, wide gap and back to narrow. Your equipment should always line up at the top and bottom with narrow gaps. Doing otherwise will leave you with a sloppy unprofessional installation.
Recently, 1-U high computer servers have become available.

## Open racks vs. closed cabinets

Open rack systems are more useful for short equipment with many wires, like hubs, switches, and routers.
Closed cabinets are more useful for deep things like servers, and when you want to lock down physical access.

## Mounting column style
### Round threaded

10-32 or 10-24

### Round unthreaded

Requires clip-nuts

### Square punched

Square-punched is often referred to as Compaq-style.
Square-punched requires the use of clip or cage nuts and can be inconvenient unless sliding rails are designed specifically for that style.
When using square-hole racks, quality nuts are very important. There are at least two styles: clip nuts have a thin metal clip that clips over the edge of the column and are easily dislodged; cage nuts clips into the square.

## Mounting methods
### Front bracket only

Used for lighter equipment, such as network devices and KVMs.

### Four post

Used for larger equipment.

### Shelf

Great for monitors, keyboards, and oddly shaped equipment.

### Sliding rail

Mounts on front and rear rails.
Sliding rails are mounted individually to the side columns and then the computer is slid into place.
Some rail mounts will interfere with center-side columns and the center columns must be removed.
Use sliding rails for mounting computers, whenever possible, as it makes mounting the hardware easier and allows you to slide the machine out for maintenance.
When using sliding rails, ALWAYS lock the computer in place with front-mounted screws or risk catastrophic tipping.
Whenever possible, when ordering equipment, specify rail mount.

## Rack Features To Look For

Always make sure shelves are available for any rack system you buy, and buy a few extra; they come in handy.
Front-column to mid- and rear-column spacing should be adjustable and is critical to easing the mounting of computers.
Always order deep cabinets, as many servers are quite deep, and you will need space for routing the wires. Cabinets should be about 32-36" deep, on the external dimension.
Some racks are connectible with a kit that removes the sides and ties the cabinets together to make an extra wide cabinet making it easier to run wires between sets of 19" racks.
Fit and finish count. Look for dangerous undebarred edges.
Determine if you can specify keyed-alike doors

## Installation Suggestions

Whenever equipment uses the rear or mid-rails, try to keep the same type of equipment in the same rack.
When mounting many odd-sized units in one rack, consider using shelves instead of rail-mounts.
Always mount equipment in such a way that the side of the box that needs access to the cables is on the same side. This means most hubs and switches and some routers should actually be mounted on the rear rail. This means you don't have to pass cables from front to back of the cabinet.
Use large-head Phillips-head screws, called truss head in catalogs. Better yet are rack specific screws. These are truss head screws that have a unthreaded portion to help align the screw. Do not use thread-cutting screws with little teeth on the tip of the screw, as sold by some network equipment companies. You can cross thread these and ruin your threads.