I was recently asked about building a power efficient server, and it seemed like a good idea to share my advice with a wider audience.

Anyone who has to deal with a hosting facility very likely knows the crunch that they’re running into with power. A standard rack may only have 42 rack units in it, but you’ll be lucky to be able to fit and power 15 servers in that rack, on a standard 30 amp circuit. If you’re careful in planning, I can help you get squeeze a bit more into that rack. I won’t advocate any particular server vendor, but I do believe that you’ll have more flexibility with a custom white-box builder, instead of going with one of the (often pricier) big name vendors.

Overall, you want to lower your power draw per server. With some careful planning, you can lower your power consumption by a fair bit, and still get the same power per machine. Here are a few things to consider:

• Can you go with a low power processor? You can often save 30 watts (or more) per core by going with an energy efficient processor.   I’ve heard it said that performance will suffer, but in my experience, if there was a loss of performance, it was minimal.
• Have you sized your memory appropriately? Every stick of memory increases your power draw.   Individual cases may very, but you should consider if you want half the number of higher density chips instead of twice the number of lower density.  On a packed server, this can save  you up to 10 watts per stick of memory.
• Have you removed unnecessary components? Every PCI card you have in the box increases the power draw.    If possible, for servers in a datacenter, go with a motherboard that has an on-board video card, and try not to add additional cards to the server.
• Did you get the right power supply? Often, you’ll get the cheapest supply that fits in the cabinet.   If you can, request a power supply that is 80+ certified.   This means that you’ll get a power supply that is 80% or more efficient.   The standard power supplies that you would have gotten may only be 65% efficient.   Being able to save 15% of your power for a small amount of money usually has a payoff fairly quickly.   In addition, you’ll have less problems with heat, and the box should generally run better.
• Have you sized your power supply appropriately? Power supplies work most efficiently when they’re close to loaded capacity.   A power supply that is 80% efficient is likely only that efficient if it is loaded to 80% or more of it’s capacity.   I often see 1U servers that draw 200 watts, but have a 450 watt low-efficiency supply in them.    Replacing the old supply with a newer, 80% efficient 250 watt supply should bring your power draw down a fair bit.

Of course, you don’t need to do all of these to optimize your rack, but every little bit counts.   The most difficult is sizing your power supply appropriately.    You won’t know how to size your power supply until you’ve done all the other optimizations.     Using a low power processor will likely be the costliest option up there, possibly adding several hundred dollars to the cost of the server.    All of the other options will raise the price a bit, but the cost should be negligible, especially if it lets you get more out of a cabinet, and keeps you from having to buy additional cabinets to hold your boxes.

Tags: 1U, data center, datacenter, hosting, power efficient, rackmount, servers