In previous server processor reviews, we've always covered the mainstream processor SKUs. Today, we're going to take a look at the low voltage parts that both AMD and Intel offer. Intel uses the LV nomenclature for their low voltage parts, and AMD uses HE to designate their low voltage parts. Both Intel and AMD have been shipping low voltage parts for a few years now, but it hasn't been until recently that these parts have started to see some growth in the industry.

The first question you may ask yourself is, "What makes a low voltage part?" A standard Intel Xeon (Woodcrest) is rated at 80W TDP, and their low voltage parts are rated at 40W TDP. Most of AMD's Opterons operate at 85W TDP and their low voltage parts come in at 68W TDP. At first glance, it would appear that Intel servers should utilize less power than AMD, but that would be an incorrect assumption. Given the many components that make up a server (especially memory), and the difference in how each vendor handles their different power states, there is more to low voltage than meets the eye.

If you've kept up with environmental and energy sector news, it's no wonder that low voltage parts are starting to gain traction in the market place. Energy costs are on the rise, data centers are out of power, and corporations with large-scale server deployments are looking to cut operating costs wherever they can. In one of the MySpace architecture videos from MIX, the CTO of MySpace detailed the evolution of their architecture; he stated that as low voltage processor parts come out they are buying them as quickly as possible. Obviously MySpace is in that percentage of corporations with a massive amount of servers deployed in data centers (6000 web servers to be exact) as detailed in a recent video from MIX07.

Due to the popularity of low voltage parts, getting a common server configured with low voltage processors is painless. Take Dell for example: when you customize a Dell PowerEdge 1950, you have the choice of regular parts or LV. Cost-wise, an LV part will tack another $350 US onto your total bill as of July, 2007. As for an equivalent AMD system, the Dell PowerEdge 1435 allows the same selection of low voltage parts, and that will tack another $200 on to your total bill. So, buying these parts is easy, and by pure technical specifications they appear to have the ability to save you some serious money. Read on, and we'll give you information that should help you decide for yourself if low voltage parts are in your future.

Benchmarking Low Voltage
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  • DeepThought86 - Tuesday, July 17, 2007 - link

    Based on these results, it looks like even though Barcelona will top out at 2.0 GHz but with the same TDP, it should be a killer in performance/watt and a great server processor
  • LTG - Tuesday, July 17, 2007 - link

    Not for long - how hard would it be for Intel to come with a non FB-DIMM solution?

    Then they would crush AMD because the CPU's actually have better power consumption.

  • Hans Maulwurf - Tuesday, July 17, 2007 - link

    The AMD numbers for power consumption of CPUs only seem far to high.

    I guess you didnt rearrange the memory modules when you took one CPU off the system. Thus you disabled half the memory modules as well.
  • Ross Whitehead - Tuesday, July 17, 2007 - link

    We did not rearrange the memory modules as we oly wanted to alter one attribute of the system between measurements so that we could attribute all difference in power to the one change.

    If you consider that all of the AMD DIMMs only took 8 Watts total, and that the difference between AMD CPUs and Intel CPUs was 31 Watts total, I am fairly confident in the numbers.
  • TA152H - Tuesday, July 17, 2007 - link

    Are these articles really meant to mislead people, or are there actual performance differences between the low voltage parts and the normal ones. I was under the impression they were the same parts but were picked for their ability to perform at lower voltages, thus their IPC should be completely identical. But the charts do show some difference, which is kind of surprising. This makes no sense to me at all, considering what AMD has been saying, but it is possible. Do you guys know what's going on with this? Are they just cherry picked CPUs that run with lower voltage, or do they differences that would alter IPC (most likely the L2 cache). It might be that the test variances are just statistical scatter, but if this is so, it would make no sense at all to report performance data on both types of processors, so I don't get it.

    Also, the reason you don't combine servers is fairly simple, and that last paragraph is mind-boggling it's so uninformed. If you run a server at 3% all day, except for say 30 minutes, and then your servers get pegged out, you might average 7% for the day, but for those moments when your two servers are getting hammered, you can't possibly merge them or you'd potentially suffer degraded performance. It's not the average that matters as much as the maximum, unless you can tolerate the degradation. Most people can not, and the cost of a server doesn't validate a loss of performance during peak times.
  • Jason Clark - Tuesday, July 17, 2007 - link

    Typically low power processors are picked based on yields, you are correct.

    The assumption about combining servers is just not correct. If you look at an enterprise VM stack like VMware, they can move VM's around based on resource usage. If a VM is using most of the resources it can shuffle the other VM's around as required. Furthermore, VMware can allow for resource scheduling, whereas you can inform the stack that at 3:00AM this VM needs more resources... Just because you spike at 80-100% for 10 minutes by no means that you are now tied to being on one physical host...

  • TA152H - Tuesday, July 17, 2007 - link

    On the first part, you should remove one of the pairs of processors, either the lower power, and say what you just said. The fact you test both for performance strongly implies a difference where none exists, and in fact is just confusing. Why test both if they are the same? Wouldn't it be better to just say they have the same IPC, and clean up your charts some (except for the cost per watt type), and remove this source of confusion?

    OK, with regards to VMWare, where do you get these extra resources from if you have gotten rid of the machine? Software is great, but if you don't have the hardware, how do you allocate these machines? I guess if you have a situation where one piece peaks at one time during the day, and another at another time, you could do something like this, so I'll grant you that it would work in some situations. In my experience, this is not typical though, and most of the time, you have "peak" hours where more people are just on and using all the servers more. And if you don't have the extra capacity sitting around on an underutilized server, there isn't much that will help it.
  • Alyx - Tuesday, July 17, 2007 - link

    In regards to saving money with servers I'm sure that substantial amounts of cash that would warrant an upgrade of this type would only be called for in a case where there was some type of a server farm or at least enough servers to consolidate one or two. Saving $10-$20 a month on power would only be useful if you were saving it on 20+ servers.

    Hell, if you are only swapping out one or two servers then the number of tech hours spent are going to eat up any monetary benefit for at least the first years worth of power.
  • VooDooAddict - Tuesday, July 17, 2007 - link

    If you can consolidate with VMWare / Xen, ect. You'll get far better raw system power usage out of a couple Dual Socket Quad Core systems running as hosts then running them all on physical with low voltage chips.

    Cooling is another issue those as once you get all those 8 Cores working on VMs you'll have quite alot of heat in a concentrated area.
  • duploxxx - Tuesday, July 17, 2007 - link

    Well it will be depending on you're hardware. If you mean current available quadcore offers, for sure they do look interesting prise wise but are not interesting performance wise in a virtual (hypervisor) environment. Even current woodcrest system have a major FSB limit with there dual 1333FSB against current AMD k8 opteron systems, in quad core cpu systems you just add raw cpu power on the same limit.

    there are enough benchmarks providing this info and if you have the chanche to play with those systems, you will even notice it.

    For real quadcore advantage you'll have to wait for the K10. Even if it is only at 2.0 GHZ with his updated dual mem controller, internal communication, shared cache and most important NPT feature it might even outperform 2.6-3.0 Clovers in virtualization.

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