Aside from chalking, talking, designing and evangelising about the exciting things such as the whizzy storage bits, new blade technologies and the wonder that is unified fabric; I also have to drop back into my corduroys and sandals to get down and geeky with some of the more fundamental elements of the data center. One in particular being.. power.
As much as the network, the storage and all these other elements are pivotal in any solution without paying close attention to the life force behind all of this, we might aswell be selling rocks.
This isn’t going to be an extensive post, just enough to cover a few principles.
Ok, so we’ve put together a high level design, we’ve worked out how the servers talk to each other, how the get their storage, how they see the outside world and how we make sure this we stop our little world from falling over should we suffer a failure. What else is there ?!
Lets throw a few scenario’s out there and get to the point. You are a project manager and under strict deadlines to get your infrastructure implemented in time for a new global application going live. You get your pallets of hardware in good time and your engineering resource is all booked in.. fantastic.
So, next step.. avoid aggravating implementation engineers and project manager alike by following a few key points :
Establish whether your inrack devices require C20 or C14 ports on your PDU, then ensure your PDU will accommodate this. Also make sure you have specified power cables for cabinet power when ordering your devices. (running around after power cables can be annoying when running behind on network configuration).
Ensure that your PDU’s will support the power draw of the device when they cycle. Normally vendor specifications should show the cycle power draw and the operating power draw. If you want to turn everything on at the same time, you need to pay attention to the first one.
Make sure that you are matching the current and phase requirements of your PDU’s with the power you are driving to the rack. Many organisations will run 3 phase power to the room, then single phases to the rack. If you have a rack full of blade servers, you may need to drive 3 Phase power to the rack and most likely 32 Amp (unless you can cram 4 PDU’s in each rack with a little bit of creative cable management, although be warned 16 Amp PDU’s tend to be light on C20 connections).
Make sure that if you are running IEC type commando power connections to the rack, you don’t go and specify PDU’s with NEMA power drop’s. A bit of communication between your electrician and they guys specifying your PDU’s can solve save a world of pain.
If you run a global operation ensure your map the power and current requirements to the countries of deployment. There is a page on my site which maps some of these requirements.
So, A little bit of maths :
To determine what power load you can support on a PDU, it goes something like this :
Single phase PDU
Current (Amps) x Input voltage = Watts
So for a single phase 32 Amp PDU in the UK, we would see:
32 x 230 = 7.36 Kw
For a 3 Phase PDU we need to find our input voltage, which is the output voltage multiplied by the square root of 3 (1.73), so for a UK 3 Phase we would have 230 x 1.73 = near on 400 (398).
We then take our input voltage (400) and multiply this by the current (lets say 32), then multiply by 1.73 again, so :
(230 x 1.73) x 32 x 1.73 = 22 Kw.
So get the power cycle and operating power draw information from the vendor (or do your own testing). Check you have the right power connectivity and size accordingly.
Then all you have to do is ensure you balance the power between your PDU’s while providing some redundancy (don’t plug both your server PSU’s into one PDU !!). Also remember that your blade chassis may have 3 powers supplies in it for N+1 redundancy to protect you from PSU failure, but if the PDU with 2 x PSU’s plugged into it fails, then you’re buggered, so you may want to add that magic number 4, to give you grid redundancy.
So, there we have it, a somewhat rambling of a post and most likely telling a whole load of people how to suck eggs… but if I can save just one project manager a headache, its worth while 😉