Low Power Server CPUs: the energy saving choice?
by Johan De Gelas on July 15, 2010 4:54 AM EST- Posted in
- IT Computing
Translated to the datacenter
Before we make any conclusions based upon what we learned in this testing session, we should not forget the lessons learned from previous experiments. And those tests tell us that you should avoid the low end server CPUs: those are the most leaky ones, consuming more power at idle and low load.
Our conclusion on our new energy measurement methodology is:
1. Low power Xeons save power but do not save energy in a typical Hyper-v consolidation ratio. Power is “capped”, but the total energy consumed for a certain task is (more or less) the same.
2. X-series Xeons offer a much better performance per watt ratio, but at the expense of brief power peaks. They do not necessarily need more energy in the long run than the lower power versions, and offer much better response times if your application is CPU bound.
So if you have to pay the actual energy consumption, you have some amp headroom left before being penalized and performance matters to your users, the faster Xeons are the right choice. The benefit is that you can offer a lower response times to your users, even when the CPU is not running at peak load! The Xeon X5670 is more flexible.
In case you pay a fixed price for a fixed amount of amps and you get heavy fines in your mailbox if you briefly breach your amp limit, buying lower power Xeons is probably the way to go.
Then again, we are not very enthusiastic about power capping at the server level. Many companies have already embraced the idea of a Dynamic Scheduled Virtualized Cluster. VMware's vSphere product is the most mature here: it is pretty easy to build a virtual cluster with dynamic power management (DPM) and scheduling (DRS). We still have to investigate this, but if this virtual cluster works well with solutions such as HP Insight Power Manager or Intel’s own power node manager, the faster Xeon will get interesting once again. The basic idea is that you should power cap your entire cluster (or rack), not one server. You should not care that one server needs a little more power than usual, but the whole cluster should not exceed the amp limits described in your contract with the datacenter. That way you can reconcile low response times with low power bills.
A big thanks to Dries Velle for assisting us in the Sizing Servers Lab.
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cserwin - Thursday, July 15, 2010 - link
Some props for Johan, too, maybe... nice article.JohanAnandtech - Thursday, July 15, 2010 - link
Thanks! We have more data on "low power choices", but we decided to cut them up in several article to keep it readable.DavC - Thursday, July 15, 2010 - link
not sure whats going on with your electricity cost calcs on your first page. firstly your converting current unnessacarily from watts to amps (meaning your unnessacarily splitting into US and europe figures).basically here in the UK, 1kW which is what your your 4 PCs in your example consume, costs roughly 10p per hour. working on an average of 720 hours in a month, that would give a grand total of £72 a month to run those 4 PCs 24/7.
£72 to you US guys is around $110. And I cant imagine you're electricity is priced any dearer than ours.
giving a 4 year life cycle cost of $5280.
have I missed something obvious here or are you just out with the maths?
JohanAnandtech - Thursday, July 15, 2010 - link
You are calculating from the POV of a datacenter. I take the POV of a datacenter client, which has to pay per amp that he/she "reserves". AFAIK, datacenters almost always count with amps, not Watts.(also 10p per KWh seems low)
MrSpadge - Thursday, July 15, 2010 - link
With P=V*I at constant voltage power and amps are really just a different name for the same thing, i.e. equivalent. Personally I prefer W, because this is what matters in the end: it's what I pay for and what heats my room. Amps by themselves don't mean much (as long as you're not melting the wires), as voltages can easily be converted.Maybe the datacenter guys just like to juggle around smaller numbers? Maybe the should switch over to hecto watts instead? ;)
MrS
JohanAnandtech - Thursday, July 15, 2010 - link
I am surprised the electrical engineers have not jumped in yet :-). As you indicate yourself, the circuits/wires are made for a certain amount of amps, not watts. That is probably the reason datacenters specify the amount of power you get in watt.JohanAnandtech - Thursday, July 15, 2010 - link
I meant amps in that last sentence of course.knedle - Thursday, July 15, 2010 - link
Watts are universal, doesn't matter if you're in UK, or US - 220W is still 220W, but with ampers it's different. Since in the Europe voltage is higher than in the USA (EU=220V, US=110V), and P=U*I, you've got twice as much power for 1A, which means that in USA your server will use 2A, while the same server in UK will use only 1A...has407 - Friday, July 16, 2010 - link
No, not all Watts are the same.Watts in a decent datacenter come with power distribution, cooling, UPS, etc. Those typically add 3-4x to the power your server actually consumes. Add to that the amortized cost of the infrastructure and you're looking at 6-10x the cost of the power your server consumes directly.
Such is the fallacy of simplistic power/cost comparisons (and Johan, you should know better). Can we now dispense with the idiotic cost/KWH calculations?
Penti - Saturday, July 17, 2010 - link
A high-performance server probably can't be used on 1A 230V which is the cheapest options in some datacenters. However something like half a rack or 1/4 would probably have 10A/230V, more then enough for a small servercollection of 4 moderate servers. The big cost is cooling, normal racks might handle 4kW (up to 6kW over that then it's high density) of heat/power just. Then you need more expensive stuff. A cheap rack won't handle 40 250W servers in other regards. 6 kW power/cooling and 2x16A/230V shouldn't be that expensive. Any way you also pay for cooling (and UPS). Even cheap solutions normally charge per used kW here though. 4 2U is about 1/4 rack anyway. And like 15 amps is needed if in the states.