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In a DataCenter, say a rack is 42U high. Some rack servers in that rack can be full-width and 1U high, while some servers can be half-width and 2U high. Yet others can be half-width, 1U, but double depth.

In all cases, the "volume" or "capacity" of these servers are same : 1x1x1 or 0.5x2x1 or 0.5x1x2 = 1 ; Hence all are equivalent in some sense.

Why Designers will choose these Dimensions ? What are the considerations involved ? Technical , Mechanical , Thermal , Economics , Business ?

Stating in other words : What are the benefits of 1x1x1 versus 0.5x2x1 versus 0.5x1x2 ?

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You're getting your terms wrong sorry.

A blade server is a physically small server that fits inside a larger chassis that provides the blade servers inside it with common services such as power supply and fans.

Here's an example of a blade system;

enter image description here

I think what you're talking about is what are called 'rack mounted' servers, or 'pizza box' servers as we call them.

Again here's an example of one;

enter image description here

Now these generally come in full-width (19 inch) format and usually come in either 1U (4.5cm) or 2U (9cm) versions (though there are larger ones for special requirements).

There are some unusual variants as you've pointed out - usually to fit certain functions within certain space/power/cooling requirements - we used to use these very odd HP SL servers that were half-width to get lots of CUDA cores in a rack but that was a very odd/rare requirement.

One area where unusual pizza box servers have been used in the past, though I'm not sure that's still the case, is in the big cloud providers. They sometimes have their servers made to their exact spec and sometimes these can be physically very small as they know what options are needed. This means they can get more into a rack if they're half-width/half-depth etc. This is an odd requirement to be honest.

Generally you should stick with 1U/2U servers, they offer 99% of the functionality and flexibility that 99% of people need - they're the VW Golf of the server world - but be aware that they are other options if you find yourself under some form of physical constraint.

  • I will edit my question with correct terminology , thanks for pointing that out. I agree about making the server as small as possible, but here I am asking about 3 cases where the capacity is exactly the same : What benefits are there for each of these 3 cases ? – Prem Jan 12 '17 at 13:48
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    Maybe link to the actual products so we can answer correctly – Chopper3 Jan 12 '17 at 13:50
  • hmm good point : I will try to add the specific rack servers to my question. – Prem Jan 12 '17 at 13:52

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