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'Case-less' Rackmounts and Multi-Machine Power Supplies?
phungus asks: "I'm looking for manufacturers of rack-mounted 'case-less' system trays for a project I'm researching. I'd like to rack-mount all of our dedicated servers without using cases. Ideally, you could put all of the components on one tray. I'd also like to find out if anyone knows of manufacturers who make big multiple-machine power supplies (ATX) so that I can eliminate individuals from the picture. I seem to recall an advertisement in a Linux magazine that did exactly this but can't seem to find it anymore. It would be nice if it supported standard relay racks, but full-enclosures would be okay too."
Any one of you who's done some serious breadboaring knows what a pain in the ass cases are. I've got some friends who've done hardware for DOD projects (US Military for the acronym-impaired), and it was just a bunch of boards hung in a rack. Kinda like old telco equipment, or mainframes. Looked hokey, but that's how the military wanted it. Ventilation's only a problem if you're not passing air over the thing, and one whole side of the cases tended to be an array of fans. 5-1/4" and 9" fans, both.
Perhaps the poster (phungus) could answer this for me. Is it really a case-less setup you want, or easier access to the boards inside? Easier access, "tool-less" cases might be an answer.
Power supplies now are cheap and small, due to high demand. They are not any less efficient than a single supply would be (ie, a 70% efficient single supply would turn as much energy to heat as 20 70% efficient power supplies given the same load)
Were one machine to fail, unless you have some sort of hot swap in place, you have to shut off all the machines on the power supply.
A significant portion of your current at low voltages (3.3V, 5v, etc) are lost in the wiring from the power supply to the MB. Say your wiring is .01 ohm per foot, with 3 feet to the computer. 5V at 80A (8 MB) introduces a .8V drop across the copper, resulting in 64W being lost as heat, and the MB only getting 4.2V. (this is an exageration to show the point, were you to do this you'd have to make copper busses (say, 1/4" by 1/4" copper bar for each voltage) which would have lower resistance) Which is a main point in using high AC voltage for distribution: Higher voltage results in less losses for less copper and long distances. Don't make your power supply go for more than a few inches to your mobo unless you know what you're doing.
There are numerous other reasons, but I'd say efficiency and fault tolerance are the two biggest reasons to avoid this idea. I'm assuming that since you're considering this idea you're rolling in money, as a custom power supply (which is what you're after) of this size is not trivial.
-Adam
Some minds are like cement: Thouroughly mixed and permanently set.
Go with someone like BGW Systems for the rack mount shelves and such.
Look under "Racks" for details
Your still going to need decent cooling with an open case environment. I don't know of a multi computer ATX power supply.
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Please people, don't chew out the guy unless you know what he is talking about. Many of you clearly don't; these are commerical products used in high-end computing applications. Remember that there are many products that really exist, even though you can't buy them at CompUSA.
This is a very good way of building a server. The ElCheapo power supplies that come in PC cases are not only inefficent, they fail frequently and take out everything downstream.
The single power supplies used in these racks are overengineered to the point that they don't fail in this manner. The racks usually have front and back doors and a blower...one we have where I work has a side-mounted McLean air conditioner! They are better cooled than any little PC box.
As far as manufactures go, I don't know. Some used to advertise in Linux Journal (which I have not taken for a couple years) but many of the designs used one-supply-per-rack, which I really don't care for. I like a single, decent-quality supply more than 24 crummy ones. I recall that 24-per-rack seemed to be the maximum you could fit into a rack...this would make each one about two rack units high, which seems to be the smallest I can imagine. They were using Intel all-in-one MBs with integrated 10/100 and VGA, with Black Box KBM switches. I would use the Belkin switches myself due to $$$.
Most seem to have rolling ventilated shelves with a IDE drive on each shelf.
Ours here at work has no identifing marks except "McLean" on the air conditioner, but as McLean is a famous rack blower manufacturer I would think they just made the air conditioner, not the rack. The rack was just shipped in from a company called "NetVantage" that we bought, so I can't tell you anything else.
I will check when I get home, I seem to recall I ordered brochures from some of those companies.
Okay, I know what you are saying, but I still like larger supplies. The cheap supplies fail a lot %-wise compared to "real" power supplies. In particlar components like the fan.
To be fair, I don't think you really need a fan in most of these racks; the PS would cool well enough through convection. But most of the supplies use cheap components that fail at a pretty alarming rate. The only large PC network I set up lost a lot of power supplies, and I bought the better ones.
Though a larger supply may be no more efficient, the sort of supplies used in large computers tend to fail pretty infrequently, and uptime may be more important than power use. Plue, if 20% of the cheap supplies fail in five years, and you have 24 of them chances are you will lose five computers over that time. A single hot-swap box (see below) probably has a failure rate in the low single digits...even if it is as high as 5%, 2 x 0.05 is a lot lower than 24 x 0.2, if you see what I mean.
Plus, with a single supply you can mount the supply in the unenclosed portion of the rack and blow the heat into the room, not mix it into the air circulating in the computer-portion of the case. Also, this allows you to keep the AC even farther from the computer--which is nice if noise is a problem. I use one computer that not only has the PS in a shielded portion of the case, it is a linear power supply. Very heavy and a lot less efficient, but the +5V line is rock-stable on my scope.
As far as failure tolerance, while a single supply does provide a single point of failure most high-end systems use multiple hot-swap supplies. The network gear I help design uses four supplies but can run on two (or one with minimal blades). With more than one supply you get load-balancing, but it lets you hot-swap without a problem.
Now, the voltage drop is a good point. I've run +5V quite a ways, and frankly with multiple 16Ga wires the drop is not even worth talking about, even in a double wide rack (one machine of mine runs 5V through a four-wide rack with no significant drop). Mini- and mainframe computers do this all the time. While newer machines use a PS-per-cage, look in the back of a pdp11/60 or a big HP9000/800 sometime. There is a 5V supply you can spot weld with! If it is a design that powers a single cage, you can use sense lines to regulate the voltage at the backplane...although not in this case. Remember that 5V can wander +/- 250mV with no problem for many designs.
Now, with 3.3 volts the voltage drop could be a concern. I don't know how the rack companies do it; one way would be to put an "industrial brick" type DC/DC converter from 5-3.3V on each shelf. You could heatsink it to the shelf and not generate too much heat. I don't know how they deal with that issue in the commerical products.
Rackable (http://www.rackable.com has some really nice high density rackmount systems with interesting cooling and wire management features. If you want you can get the systems without top or bottom covers and they can be installed tray-like into the rack.
They have 1/2 width 1U units that can go dual CPU which means you can get 88 dual-processor systems in a single rack :)
Actually, you need the case if you plan on using the standard fans - without the case, there will be no even circulation of air around the motherboard. It's a common mistake, but leaving the case off a server can actually make it more prone to overheating.
"Flamebait"?! What the heck was that for?