Server Case Hardware Guide

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   Server Case Hardware Guide
Choosing a server enclosure is much more important than choosing a desktop case.  Different server enclosures accept different sized motherboards, different numbers of HDDs, and can accept different hardware like multiple PSUs and add in cards.  This guide will show you the differences between different sized cases and the differences between cases of the same dimensions.
Standard Sizing

Almost all server systems follow a certain standard sizing called rack units.  

A rack unit is a unit of measure used to describe the height of a server, network switch or other similar device mounted in a 19-inch rack or a 23-inch rack (refers to width of rack). One rack unit is 44.45 mm (1.75 in) high.  One rack unit is commonly designated as "1U"; similarly, 2 rack units are "2U" and so on. The size of a piece of rack mounted equipment is usually described as a number in "U". One rack unit is also sometimes referred to as "1RU"; most server racks have 42 U of height. 

Half-rack units typically describe units that fit in a certain number of rack units, but occupy only half the width of the rack (9.5 inches or 241 mm). For example, a "4U half-rack" DVCAM deck would occupy 4U (4 × 1.75 inches) height × 9.5 inches width. In theory, two half-rack decks could occupy the 4U space.

Differences In Rack Cases

1U Rack Case 
At only 1.75" tall maximum, there is very little room except the essentials in this server size.  Special low profile CPU coolers and small diameter fans must be used to cool the system and may produce very high levels of noise.  Hard drive space is also a concern as many cases in this size can hold at maximum 3-4 3.5" HDDs.  Up to 8 2.5" drives can be used if the system accepts them.
Due to the small size, this is a great form factor where maximum density of CPUs and HDDs is needed.

2U Rack Case 
With more space in the case, less expensive components can be selected that do not need to be height restricted.  Also there is more room for disk space, memory, and even optical drives.  Usually there is also room for 1 or 2 side mounted expansion cards.

3U Rack Case 
This case allows for the maximum amount of upgrades and add-ons such as more hard drives, more CPUs, maximum amounts of memory, and even lower-noise cooling systems.  This case size allows for very powerful systems and also allows for full height expansion cards.  This is a great case were video cards or other expansion cards need to be added to a server system.

4U Rack or Tower Case 
Notice how this case is in a tower configuration.  Most desktop cases are about 4U in width and thus the 4U height cases can also be used as a tower server.  Due to this interchangeable configuration, this sized case can either make a very powerful rack server or an inexpensive desktop server.
Like the 3U case, maximum amount of upgradeability and add-ons while also being much quieter than the smaller server cases.
Unlike the other rack cases, this case size is also used in desktop servers, where clusters of more than 2 server are not needed.  Perfect for the user that needs a single server, but wants to use rack server components which a normal desktop case cannot fit or use.

Server Case Features

Hot Swappable Hard Drives 
Almost all server cases have this interface built into the case.  This allows the server administrator to change old or failed hard drives without disassembling the server or powering it down for maximum up time.  If a server does not have this feature, then the server should not be used in data sensitive environments or where the server must be up 100% of the time.

Room For Professional Hardware 
Certain applications require the use of certain professional hardware which is normally more powerful and larger than consumer versions.  While consumer video cards are reaching 11" in length, professional video cards are reaching over 14" in length.  Many server cases have the room and motherboard layout to accept these larger than normal components that normal desktop cases would not be able to fit.