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Thread: Power Question

  1. #1

    Power Question

    How much does power generally run and how much can the max for a cab handle?

    Basically, I have 1Us that suck up a max of 4.2 A and 2Us that use a max 5.7 A (115V) (according to our vendor)

    Does that mean I should only put about 8-10 servers in a rack because the max is about 40A? I know they dont max all the time but they will at peaks.

    How do you fill up your racks?

  2. #2
    You will run in to cooling issues when you are using over 3500 watts of power, roughly 30 amps, in cabinets. This is without any additional cooling features like the doors that are one big fan, etc. There are ways to optimize the cooling of a cabinet based on equipment installation. For instance, if you are having cooling issues make sure you have spacers or equipment in every U from top to bottom. This helps keep your exhaust from getting to the intake. Normally this is not an issue, but if you are planning on getting the most equipment possible in a cabinet you may run into some issue. Your provider should be able to help you with this.

    If you are concerned about cooling you need to go to the facility and check it out. If it is hot your gear is going to be hot. Many facilities have not kept up with their AC needs. I have even seen pics on WHT of a colo that takes sides off servers. I thought it just meant the customer didnt send sides or something, but when they shipped a customer's server to us the side didnt match the case. What a joke. Cooling is part of what you are paying for with power. If you are going to be doing a rack or cabinet you really need to go check out the facility or talk to someone that has been there.

    When the vendor tells you the max it doesnt normally mean you should expect it to use that under normal operation. Sometimes the vendor is just telling you it has a 500 watt power supply so the most it could pull is a little over 4 amps. You dont really know until you check the server under normal load. You need to leave some room on your power to account for spikes caused by high usage. Back when slammer hit a lot of outages were caused by servers pulling significantly more power and tripping breakers. As a general rule you should stay under 80% utilization on a breaker.

    In Dallas the rate has been $8-12/amp for several years. The utilities have gone up significantly in the past 5 years but most providers have held their rate to the customer. You also need to make sure that you are getting UPS and generator included on that power.
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  3. #3
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    Power varies from $150 to $400 per 20 amp circuit depending on the geographic location, quality of the data centers UPS and generator, and mark-up.

    Utility power is highest in NY and CA. However, raw power costs are only a portion -- the other portion is amortizing the UPS and generator infrastructure.

    There was a colo in NY that designed their electrical and HVAC for a heat load of 180 watts per square foot a few years back, which was unheard of at that point in time. The electrical worked great; the HVAC compressors worked great, the ventilation simply could not remove the heat from the cabinets.

    In order to get the heat out of the cabinets, you need to move air through. The more heat, the more air. and the higher the air velocity, as the hole in the floor (or cabinet fan on top) is constrained. (Unless you go with cold air distribtion, which gets expensive and also leads to static problems)

    And of course everyone wants to get their moneys worth out of the cabinets, so they install full length servers in the cabinets, which block the air flow.

    And some data centers simply have lousy air distribution.

    So you need to get a systems approach. One server company started building rack mount servers with no top or bottom, so that air would flow from bottom to top across the motherboard and hard drives. Works great where you have raised floors.


    There are companies out there running 40 1U servers per rack with no issues, and companies running 20 1U servers that are losing hardware due to heat

    What I am driving at is how you fill up your racks is a function of the data center HVAC system, the type of servers that you have, how efficient your power supplies are, etc.

  4. #4
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    Re: Power Question

    Originally posted by SB001
    How much does power generally run and how much can the max for a cab handle?
    20A of power runs from $125/month to $400/month, depending on where you go.
    I have seen cabinets holding 60A worth of gear, but they've had a lot of cooling to back it up.
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  5. #5
    I would say you cost per 20amps of 120 volt power should fall in the 175-400$ a month.

    In a full cab with 1 U's top to bottom with perferated doors and 4 fans in the top I have customers pulling 60 amps of power in a single full cab across 4, 20 amp power strips.

    It's a hot cab FOR SURE. But it can be done, make sure all your cases suck from the front and blow out the back. Make sure you have cold air comming in the front and the hot air can escape out the top and back.

    Best of luck.

  6. Running 220V will of course, reduce amperage significantly.
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  7. #7
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    Originally posted by [email protected]
    Running 220V will of course, reduce amperage significantly.
    Sure, but you'll still be using the same number of Watts
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  8. Yeah... I'm just talking from a cost perspective, often.
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  9. #9
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    Interesting reading about the power, but I'm wondering about the 60A.

    A full cabinet is about 42U , you've mentioned that some clients are doing 60A.

    Assuming this is 110v grid, then total watts are 6600 watts

    Any server nowdays should have at least 350W power supply with peak usage of about 75% ? so 260W

    If I divide number of total watts on per server usage, this give me around 25 servers in that cabinet, am I right ?

    My guess in here is that they're either using all 2U servers, or they're using 1U servers with empty spaces between them.

    Any recommendations on where the fans are best placed on the cabinet for keeping the cabinet in good condition ?
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  10. #10
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    Originally posted by tamouh
    Any server nowdays should have at least 350W power supply with peak usage of about 75% ? so 260W
    Your power supply shouldn't draw peak current all the time. For example, I have a 500W power supply in a mini-tower in my office, but I've measured it on a managed PDU that reports 1.6A 110VAC draw. If I added some disks, used the CD drive, or used the CPU heavily the current draw would increase.
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  11. #11
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    Originally posted by [email protected]
    Yeah... I'm just talking from a cost perspective, often.
    Any provider that doesen't charge double (per amp, or darn near it) for 220V over 115V is doing something wrong in their math generally speaking.

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