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Dear serverfault knowledgeables, im in a decision dilemma right now, which I can't resolve due to lack of hands on experience.

I need to build a testbed for basically virtualizing a LAMP application (os'ses not yet decided) including server side calculations. I'll opt for XEN since it seems better supported by cloud hosters at the moment. The hardware is for a proof of concept for a startup doing saas and might be used for closed live alpha/beta later on.

After testing, the testbed might be

a) deployed as a colocated white box server

b) used as workstation

  • Single socket is enough.
  • We want to have ECC memory for reliability, this excludes most of the consumer line at intel.
  • If intel CPU, then threaded cpu (HT) is preferred
  • have at least 16 gig ram
  • If justified by price and reliability is not too bad, a high quality desktop MB instead of a server MB would be worth a try

It came down to the opteron 6128 vs. the xeon 5620 for me after a lot of research, but I don't necessarily have to be right.

Which CPU is preferrable, concerning TCO (MB price, power requirements 24/7...) , Opteron 6128 or Xeon 5620? Which one offers better performance in real world applications? (Do You have any other suggestions I probably overlooked?)

Thank You for Your consideration

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6 Answers

"14.4GByte/sec memory bandwidth given that it has two memory channels, or about 1.8GByte/sec per core."..."with Intel currently providing lower [full] core counts that are kept fed with with more main memory bandwidth (in total and per core)."

Sorry, i don't understand. I researched a few hours now and I might be wrong as I've been out of the processor talk for years now, but serverfault, Anandtech, wikipedia (sorry), even PCPRO and AMD1, AMD2 , AMD3 state that the 6100 series (MC) has 4 memory channels with high memory transfer rates ( Anandtech, Anandtech2).

Sorry, I had to [remove direct references] obfuscate all hyperlinks because of serverfault's limits on low reputation posts. Just take http://developer.amd.com/documentation/articles/pages/Magny-Cours-Direct-Connect-Architecture-2.0.aspx as main reference.

So please clarify as my maths seem to work differently, but I might be wrong:

Opteron 6100 have 2 dies per package (=processor housing) and 1 memory controller per die AMD, being 64 bit wide and running at 1.8 GHz Anandtech, where my maths gives me 64 Bit bus times 1,8 GHz per mem controller (=per die) = 14,4 GB/s per die, not in total, which at 4 cores per die gives 3.6 GB/s per core (if all cores are equally stressed).

So the Opteron would have more memory bandwidth per core than the Xeon per thread. Also the complete opteron processor would have 28.8 GB/s memory global bandwidth, which is higher than with the Xeon part.

Thanks for any clarification.

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Are you looking for absolute power or value here? your question suggests the latter but now you're interested in top end detail - I don't understand. –  Chopper3 Jun 22 '10 at 15:36
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Your path of least resistance might be to hop onto ebay and buy a HP XW9400. Secondhand ones ae quite cheap, although you need to make sure you get one with the right CPU. You want Opteron 237x or 2380 CPUs - 2200 series Opterons don't support nested page tables and 234x/235x series (Barcelona) ones have a hardware bug.

If you don't mind fitting your own CPU, ones with 2200 series opterons can be bought for a few hundred dollars and you can get an Opteron 2376 for about $500 off ebay. You will need to make sure you get a compatible heatsink, but the ones in the machine will probably do fine.

XW9400s take DDR2 memory, of which there is a significant glut on the market due to overproduction. 8GB DDR2 ECC registered kits compatible with an XW9400 should cost about $250 each off Ebay. If desired, you can expand the machine to two sockets with 4-6 core Opteron chips and 64GB of RAM.

This gives you a fairly cheap development workstation with hardware VM support and pretty good quality componentry and buckets of headroom. You can put SAS or SATA disks on it, and it has PCIe -x4/x8 slots that will take most RAID controllers, should you feel the need. Note that the motherboard is an OEM version of a Tyan S2915 (IIRC).

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Some theoretical numbers:

  • Intel E5620: 2.4Ghz with 4 Cores + HT. Turbo-boost can bump that to 2.66Ghz giving approximately 12.5Ghz of aggregate CPU, maybe a bit more if your workload is very HT friendly. Up to 25GByte/sec memory bandwidth provided you populate all three memory channels with 1333Mhz DDR3, or about 6.25Ghz per core \ 3.125GByte/sec per thread.

  • Opteron 6128: 2Ghz with 8 full cores giving 16Ghz of aggregate CPU, approximately 28.8GByte/sec memory bandwidth given that it has four memory channels per socket (2 per die), or about 3.6GByte/sec per core.

Obviously not all CPU Ghz are equal and real world numbers will be a lot lower but there is a clear difference in approach with Intel currently providing lower [full] core counts that are kept fed with with more main memory bandwidth (in total and per core).

If absolute CPU grunt is what you are looking for then the Opteron will be better, if memory bandwidth per core is more important then the Xeon will be better, if your needs are somewhere in between then the differences will be less clear cut although I think the AMD edges out the Intel for your type of use cases. Anandtech has a good comparison of the 6 Core Xeon 5670 and the Opteron 6174 that compares the higher end (6 Core Intel vs 12 Core AMD) of these two CPU families but I think their conclusions will apply more or less to the two lower end CPU's you are looking at.

On the cost front the Intel CPU is more expensive (the street price difference between the two puts the Xeon E5620 about $120 more expensive than the Opteron 6124 at the moment) and it must be configured with memory in sets of 3 DIMMs in order to realise it's maximum memory bandwidth. This means that memory sizes of 6, 12 & 18 etc GByte are what you should be looking at. The AMD, having 2 on die memory controllers, performs best with the more usual 4,8 & 16 etc. If 16GByte is the minimum you require then you should factor in the additional cost of the extra DIMM(s) which will make the Intel option even more expensive.

One final detail is that the E5620 supports Intel's new hardware AES instructions that might make a significant difference if your use case makes any significant use of crypto functions that will make use of them.

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The Opteron has 2 memory channels per die, and 2 dies per package; you're numbers for the Opteron's memory bandwidth should be 28.8 GB/s or 3.6 GB/s/core. –  Chris S Jun 22 '10 at 15:38
    
Ah - good point, thanks for catching that - I got myself confused when looking at the specs. I've corrected the content. The key points remain but the bandwidth per core data point is obviously not as significant as I'd made out originally. –  Helvick Jun 22 '10 at 17:36
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When buying metal to run VMs I usually go with the lowest server class cpu I can find, and I target 2~4 gigabytes of ram per core depending on the hardware and the expected workload.

  • "server class" = Xeon or Opteron
  • "lowest" = less GHz and/or watts

You'll end up having 4 cores sitting idle most of the time waiting for disk activity, unless you have a really good I/O subsystem (big raid with lots of spindles and/or fast disks and/or SSDs, either directly attached or via SAN).

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Which CPU is preferrable, concerning TCO (MB price, power requirements 24/7...) , Opteron 6128 or Xeon 5620? Which one offers better performance in real world applications? (Do You have any other suggestions I probably overlooked?)

  • MB Price: Opteron boards are usually a little cheaper than Xeons. Here are a few to mention:
    1. TYAN S8230GM4NR Dual Socket G34 ($469.99)
    2. ASUS KGPE-D16 Dual Socket G34 ($439.99)
    3. SUPERMICRO MBD-H8SGL-F-O ($264.99)
  • Power requirements hands down goes to Opterons as long as you go for HE or EE versions. AFAIK, Opteron 6100 series only has HE (wikipedia).
  • Better performance in real world applications: This can go either way. Xeons typically do very well with data crunching operations largely in part to a larger L3 cache while Opterons typically don't have as much L3. There are other factors in the Xeons performance, but in your case, I'm not so sure it matters.

I need to build a testbed for basically virtualizing a LAMP application (os'ses not yet decided) including server side calculations. I'll opt for XEN since it seems better supported by cloud hosters at the moment. The hardware is for a proof of concept for a startup doing saas and might be used for closed live alpha/beta later on.

Okay, so this project is really a "proof of concept for a startup doing saas"? Spend the least amount of cash as you can with the most room to upgrade should it be necessary. While I admit my AMD fanboy-ish stance, I'd say for your particular situation, I'd focus less on the production/final environment of your product/service and just focus on the test bed aspect.

Budget is not just a concern, it is the primary concern so just go the cheaper route while meeting your minimum requirements (CPU, 16GB ECC RAM, etc.) which tends to work in favor of AMD as they still use DDR2 for slightly older Opterons (Istanbul, Shanghai, Barcelona). Newer Opterons do use DDR3 which is a little more costly but I'd scale things back as much as you could while having room to grow.

So for example, maybe get a dual socket board, and high density RAM (4x4GB or 2x8GB DIMMs) so that should you need to expand it's an option. Building servers is largely about budget which translates into whether you have the ability to upgrade. Seeing how this is just a test bed, keep the costs as low as you can.

Last few notes/suggestions:

  • Keep in mind, technology changes so even with your alpha/beta product in use, maybe at some point in the future you switch to Xeons. That's totally fine. But there's really nothing that you can do now to really forsee the future. Just focus on costs and upgrade path and just run with it. Don't sweat the infinitesimal details now. Startups need a lot of progress fast.

  • Don't forget about a good RAID controller as well! CPU/RAM don't mean much without some good disk I/O!

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Whilst I utterly adore Intel's 55/56xx series chips, know them to be incredibly fast and buy them all the time I have the luxury of budget - it seems value is more of a concern for you.

With that in mind I'd like to suggest a third option - AMD's Athlon II X3 440. It's seriously cheap, only has 3 cores but at 3.0Ghz, supports ECC and 16GB as well as coming in mainstream desktop form. If this is purely a PoC system why not get the cheapest thing that'll do the job?

The CPUs themselves are like $50 (5620's are >6x that) and I just spotted THIS mobo too. Hope this at least makes you think about the problem a different way.

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