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I'm looking for a good way to audit the per-rack power utilization in an existing server room. Each rack is powered, for the most part, by a pair of single phase 30A/208v feeds. Is there something like a network-accessible clamp meter I could attach to the power cords that would let me record current draw over time? Would something like the TED 5000 work for this purpose? Actually replacing the PDUs (with, say, metered PDUs like the ones available from APC) isn't an option at this time; this is part of a planning effort for a new data center, and it has to be minimally disruptive to the existing environment.

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3 Answers 3

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The problem that you're going to run into with a clamp-on ammeter is that you can't actually clamp it over the entire power cable - if you do this, you'll read a zero-amp current. Assuming that you're dealing with single-phase power, you'd need to clamp over either the hot or neutral (I'm going to assume that there's little if any current going back down the ground) to get an accurate reading.

Most of the modern servers I've worked with allow you to monitor their power draw in real-time via their iLOM/ipmi controllers. Have you looked into this possibility?

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Agreed, some stripping of the cables is usually necessary. –  Ausmith1 Dec 7 '10 at 17:19
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...which I would strongly advise against in a datacenter environment. –  EEAA Dec 7 '10 at 17:20
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Yeah, that would not be "minimally invasive". Thanks for the info. –  larsks Dec 7 '10 at 19:19
    
It all depends on how your data center is wired. If you trace the leads for the sockets feeding the PDUs back to the central input rails you'll usually find that the connections are a set of single wire leads. If the armor sheath is not too close to the rail connection point then you can fit in a ammeter clamp without any problem. If the armor sheath is too close to do this then you'll have to power down the attached PDU and have an electrician strip the sheath back a little. As long as your rack is redundantly wired you can do this without any downtime. I've done this for 20+ racks 0 downtime –  Ausmith1 Dec 7 '10 at 22:10
    
Also note that iLO/DRAC/IPMI power monitors are reading the output from the power supply to the motherboard. Add about 20% for an 80Plus certified power supply. Also also note that power on readings will be much higher than normal usage for all modern machines. –  toppledwagon Jan 5 '11 at 8:40

I'd suggest contacting your state or local governments energy efficiency entity or even your power provider. They usually have such equipment and are typically happy to come out and do such work for free or for a minimal charge.

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What's the kit in the rack? Most ISS servers should by now have power consumption data accessible via SNMP. You could use this to build a rack tally. Granted, SAN switches, Ethernet switches and the like will most likely not have such data available.

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