[Beowulf] Newbie Question: Racks versus boxes and good rack solutions for commodity hardware

John Hearns hearnsj at googlemail.com
Fri Dec 12 09:13:54 PST 2008

2008/12/11 arjuna <brahmaforces at gmail.com>

> What is 1u?
Easy question! a "U" is short for a "rack unit". Rack mounted equipment
always comes in multiples of a vertical height unit, which is 1.75 inches. I
gather this is actually an old Russian unit of measurement (you can check on
Wikipedia). So when you put equipment into standard 19inch wide racks, you
ask "how many U high is that equipment). It means that you can mix and match
different types of equipment in the same rack.

Specifically for this discussion, a 1U computer (server) is a server which
takes up 1U of vertical space.
They are generally very deep to compensate for the lack of space in height,
and use lots of small, fast fans rather
than the big one you have in a desktop.
Air comes in through slots in the front, past the disk drives, over the
motherboard and out of the rear.
These systems generally pack more compute power per piece of floorspace, and
help make the cabling neater as everything is in a standard place to the
rear of the rack.

> What is a blade system?
This is where servers are packaged into standard units, generally a bit
smaller than the 1U servers above.
The blades plug into a chassis, which in turn is mounted in the rack.
The chassis provides power to each blade, plus networking connections across
a "backplane"
In the case of the 1U servers you generally have to connect mains power to
each one, and run separate cables for ethernet / Myrinet / Infiniband. This
cabling is all wrapped up inside the chassis.
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