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Thread: DC Electricity

  1. #1
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    DC Electricity

    How do you manage your power ? Can you manage 40 Servers with 20A. ?

  2. #2
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    Quote Originally Posted by bukzrock View Post
    How do you manage your power ? Can you manage 40 Servers with 20A. ?
    Atoms, sure. That's about it.
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    Quote Originally Posted by Dougy View Post
    Atoms, sure. That's about it.
    How about Dell Poweredge and Prolant Servers ?

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    Quote Originally Posted by bukzrock View Post
    How about Dell Poweredge and Prolant Servers ?
    Brand is irrelevant for the most part. Depends on the processor(s), number of fans, hard drives, etc. A basic E3 in Supermicro 4 bay hot swap chassis will run about .6-.8 amp in my experience, depending on the current load. That's with 1-2 hard drives. Don't expect to fill up a rack with only one 20 amp circuit. If you don't mind a little extra space, you could shoot for a 30 amp circuit. You won't be able to fill the rack, but you'll be able to get 30+ servers and switches in there if you do it just right. Don't forget the 80% ratio for code. So you can only use 16 amps of a 20 amp circuit.
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  5. #5
    Quote Originally Posted by Jasonsite View Post
    Don't forget the 80% ratio for code. So you can only use 16 amps of a 20 amp circuit.
    Why do they even market it even like this? It's like if you were selling a container that says 8 quarts but it can only actually store 6 quarts.

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    Quote Originally Posted by bukzrock View Post
    How do you manage your power ? Can you manage 40 Servers with 20A. ?
    Your mileage will vary based on the equipment in your rack. Some of our racks suck up about 32a 120v (single xeons mix of 2-4 ssds/hdds), other racks suck up 24a 208v (dual xeon 1u -> 3u). You will want to use a kill-a-watt meter to get a good idea of your common configs average and peak power usage and plan accordingly. After a while you'll be able to guesstimate fairly accurately how much power to provision for your racks, and just keep an eye on things as you grow via the remote pdu amp readings etc.

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    Quote Originally Posted by HarvestMine View Post
    Why do they even market it even like this? It's like if you were selling a container that says 8 quarts but it can only actually store 6 quarts.
    While it can be confusing, they are selling you a 20 amp circuit. Same idea like a 100Mbps port won't handle 100Mbps. It's more like 90Mbps usable generally. When you buy power for single server colo, I believe they already factored in 80%. So they are then selling you 1 usable amp, rather than a 20 amp circuit.

    Hope this helps.
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    Quote Originally Posted by HarvestMine View Post
    Why do they even market it even like this? It's like if you were selling a container that says 8 quarts but it can only actually store 6 quarts.
    You can read about that here; http://ecmweb.com/basics/sizing-circuit-breaker .

    Other than it generally being a rule, it's simply a good practice because when you have a bunch of machines booting at once will use a lot more power than active/idle machines (most advanced pdus have staggered spin up options), you don't want to be tripping a breaker and having to wait for a tech to reset it, especially if their procedures require an electrician to check flipped breakers etc. Just accept that it's another one of those hidden costs of colo and price your products accordingly.

  9. #9
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    Quote Originally Posted by HarvestMine View Post
    Why do they even market it even like this? It's like if you were selling a container that says 8 quarts but it can only actually store 6 quarts.
    Most market like that, because it's part of code/law. Even if the data center wanted their customers to be foolish and run their breakers at 100%, electrical/fire/city/national codes prevent this for various design/safety reasons.

    It's incredibly foolish to run near/at 100% on breakers, because as soon as there's a utilization spike, temperature spike, reboot, incidental piece of gear plugged in [IE: KVM cart/monitor/etc.], you'll trip your breaker, and everything will be offline. 80% sustained utilization (you can always spike to 100% temporarily) provides you a quite reasonable/realistic buffer. Most servers will decrease > 20% in power when at idle, so you can still over-subscribe your circuits being below 80% utilization in a typical day scenario.
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    Amp != Amp.
    What's the voltage?
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    Quote Originally Posted by bukzrock View Post
    How do you manage your power ? Can you manage 40 Servers with 20A. ?
    Our E3v3 racks (ssd only) are setup with 35 servers and 3 switches on 208V 20AMP and we end up around 14.5AMP utilization.
    Another rack setup we have, with 25 E3v1's and 3 switches when all 25 were doing a kernel compile with a make -j8 we hit 14AMP's.
    We moved a few of the E3v1's out, and moved in some E3v3s (total servers in that rack is 29 I believe) and setup 10 of the servers with 4 x sata + 1 ssd and we ended up with 13AMPS with our typical peak utilization.
    Last edited by Steven; 12-13-2014 at 12:53 PM.
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    Quote Originally Posted by Clouvider-Dom View Post
    Amp != Amp.
    What's the voltage?
    My current powe supply is 120 Volt 10 Amp Single Phase Power Circuit

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    Quote Originally Posted by bukzrock View Post
    My current powe supply is 120 Volt 10 Amp Single Phase Power Circuit
    I was really confused reading this thread. You titled it "DC electricity", probably meaning "Datacenter electricity." I initially thought you meant DC electricity as in direct current electricity....which is commonly used in datacenters. You might want to either start a new thread or change the thread title (if possible).

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    Quote Originally Posted by Jasonsite View Post
    Brand is irrelevant for the most part. Depends on the processor(s), number of fans, hard drives, etc. A basic E3 in Supermicro 4 bay hot swap chassis will run about .6-.8 amp in my experience, depending on the current load. That's with 1-2 hard drives. Don't expect to fill up a rack with only one 20 amp circuit. If you don't mind a little extra space, you could shoot for a 30 amp circuit. You won't be able to fill the rack, but you'll be able to get 30+ servers and switches in there if you do it just right. Don't forget the 80% ratio for code. So you can only use 16 amps of a 20 amp circuit.
    Never quote power consumption in current/amperage. Quote it in power, that is, watts.

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    Quote Originally Posted by scurvy View Post
    Never quote power consumption in current/amperage. Quote it in power, that is, watts.
    OP, @bukzrock asked in relation to amps. Was trying to keep this simple for him. Thanks for the education.
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    Quote Originally Posted by scurvy View Post
    Never quote power consumption in current/amperage. Quote it in power, that is, watts.
    Problem with quoting in watts, is you're quoting for uneducated people, the concept behind obeying electrical code isn't hard to grasp.

    You quote in watts, I guarantee eventually you're going to get the idiot customer, who doesn't understand that voltage drops on a line as amperage increases, and argues you're not delivering the specified wattage as a result, etc.
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    Quote Originally Posted by porcupine View Post
    Problem with quoting in watts, is you're quoting for uneducated people, the concept behind obeying electrical code isn't hard to grasp.

    You quote in watts, I guarantee eventually you're going to get the idiot customer, who doesn't understand that voltage drops on a line as amperage increases, and argues you're not delivering the specified wattage as a result, etc.
    Watts are watts though. It's straight apples to apples. A watt is a watt regardless of circuit type. Figure out how many watts you need, then figure out the best circuit.

    Also, there's nothing wrong with educating idiot customers. It works in your favor to educate them.

  18. #18
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    Quote Originally Posted by scurvy View Post
    Watts are watts though. It's straight apples to apples. A watt is a watt regardless of circuit type. Figure out how many watts you need, then figure out the best circuit.

    Also, there's nothing wrong with educating idiot customers. It works in your favor to educate them.
    If you were educating idiot customers, you'd tell them what sort of circuit they were buying, and you'd help them understand code rules/etc.

    The problem with watts is this:

    Say you give the customer a 30A/208v circuit, and you market it (rightfully so) as 4992w. Well for starters, most people will state it's a 5kw circuit, which is entirely fair, right?

    Well, then you get that "special" customer, who is going to have a kill-o-watt meter or similar on their power, say it's 10awg, and running ~100' from one end to the other. Chances are maybe you already have some load on your PDU's/transformers, and they're putting out 206/208v, which would be entirely normal.

    Well now, the customer is going to see a voltage drop on the transformer, one on the line, maybe he's going to see 202v (as an example). The customers going to go ahead and plug 202 * 24a, and argue that he's only getting 4848w out of that 5kw circuit you just sold him, and refuse to pay the bill.

    Whose right, whose wrong here? It's not viable to sell metered/kwh circuits to every cabinet (in most areas, the requirements for metered billing are extreme/expensive/etc.), so instead you're advertising a watt value based on the circuit you've sold, when it doesn't translate to bare watts on their end.

    Alternatively, I suppose you could sell them as 4800w circuits, but who does that? It's only going to confuse the educated customers, and the uneducated that try to size their PDU's by wattage, etc.

    This may sound absurd, but I've seen it happen first hand in a *big* colo from a smaller cabinet customer. The customer stuck to their guns, threatened legal, refused to pay that portion of the bill, etc. and I remember it being one of those things that went on for months, much to the dismay of everybody (except the small customer, who was skating around without paying his power bill at all).
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  19. #19
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    You don't need to quote watts if you quote amps and volts...

    Re Voltdrop, your colo provide should be putting in big enough cables to allow you to use the full capacity of the breaker, otherwise the cable will become the fuse.
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  20. DC Electricity

    My company <<snipped>> always quotes in critical kilowatts (ckW) so anyone knows right off the bat how much power they can utilize. ckW is 80% of the actual power delivered on the circuit. porcupine nailed it earlier that 80% is industry standard primarily to handle spikes in power so you don't trip a breaker in your PDU or data center's circuit breaker.

    One other confusing aspects for data center customers is the concept of primary and redundant or secondary power. The quoted power is the aggregate power used on both circuits. For example, if you get a 4.92 ckW primary/redundant power cabinet (208v/30A) it is 4.92kW on both primary/redundant circuits not 4.92kW per circuit. This is also industry standard in case a circuit does trip there is enough power on the redundant power circuit to handle the load.

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