21st Century Server Choices

Lots of people base their server form factor choice on what they are used to buying. Critical database applications equal a high-end server. Less critical applications: midrange server. High-end machines used to find a home at larger companies and cheaper servers would typically be attractive to SMEs. I am oversimplifying but those are the clichés that pop up when you speak of server choices.

Dividing the market into who should or should not buy high-end servers is so... 20th century. Server buying decisions today are a lot more flexible and exciting for those who keep an open mind. In the world of virtualization your servers are just resource pools of networking, storage and processing. Do you buy ten cheap 1U servers, four higher performance 2U, one “low cable count” blade chassis, or two high-end servers to satisfy the needs of your services?

A highly available service can be set up with cheap and simple server nodes, as Google and many others show us every day. On the flipside of the coin, you might be able to consolidate all your services on just a few high-end machines, reducing the management costs while at the same time taking advantage of the advanced RAS features these kind of machines offer. It takes a detailed study to determine which strategy is the best one for your particular situation, so we are not saying that one strategy is better than all the others. The point is that the choice between cheap clustered nodes and only a few high-end machines cannot be answered by simply looking at the size of the company you are working for or the "mission critical level" of your service. There are corner cases where the choice is clear, but that is not the case for the majority of virtualized datacenters.

So is buying high-end servers as opposed to buying two or three times more 2-socket systems an interesting strategy for your virtualized cluster if you are not willing to pay a premium for RAS features? Until very recently, the answer was simple: no. High-end quad socket systems were easily three times and more as expensive and never offered twice as much performance compared to dual socket systems. There are many reasons for that. If we focus on Intel, the MP series were always based on mature but not the cutting edge technology. Also, quad socket systems have more cache coherency overhead, and the engineering choices favor reliability and expandability over performance. That results in slower but larger memory subsystems and sometimes lower clock speeds too. The result was that the performance advantage of the quad system was in many cases minimal.

At the end of 2006, the Dual Xeon X5300 were more than a match for the Xeon X7200 quad systems. And recently, dual Xeon 5500 servers made the massive Xeon 7400 servers look slow. The most important reason why these high-end systems were still bought were the superior RAS features. Other reasons include the fact that some decision makers never really bothered to read the benchmarks carefully and simply assumed that a quad system would automatically be faster since that is what the OEM account manager told them. You cannot even blame them: a modern CIO has to bury his head in financial documents, must solve HR problems, and is constantly trying to explain to the upper management why the complex IT sytems are not aligned with the business goals. Getting the CIO down from the “management penthouse” to the “cave down under”, also called the datacenter, is no easy task. But I digress.

Virtualization can shatter the old boundaries between the midrange and high-end servers. They can be interesting for the rest of us, the people that do not normally consider these high-end expensive systems. The condition is that the high-end systems can consolidate more services than the dual socket systems, so performance must be much better. How much better? If we just focus on capital investment, we get the figures below.

Type Server CPUs Memory Approx. Price
Midrange Dell R710 2x X5670 18 x 4GB = 72GB $9000
Midrange Dell R710 2x X5670 16 x 8GB = 128GB $13000
High-end Dell R910 4x X7550 64 x 4GB = 256GB $32000

So these numbers seem to suggest that we need 2.5 to 3 times better performance. In reality, that does not need to be the case. The TCO of two high-end servers is most likely a bit better than that of four midrange servers. The individual components like the PSU, fans, and motherboard should be more reliable and thus result in less downtime and less time spent on replacing those components. Even if that is not the case, it is statistically more likely that a component fails in a cluster with more servers, and thus more components. Less cables and less hypervisor updates should also help. Of course, the time spent in managing the VMs is probably more or less the same.

While a full TCO calculation is not the goal of this article, it is pretty clear to us that a high-end system should outperform the midrange dual socket systems by at least a factor two to be an economical choice in a virtualization cluster where hardware RAS capabilities are not the only priority. There is a strong trend that the availability of the (virtual) machine is guaranteed by easy to configure and relatively cheap software techniques such as VMware’s HA and fault tolerance. The availability of your service is then guaranteed by using application level high availability such as Microsoft’s clustering services, load balanced web servers, Oracle fail-over, and other similar (but still affordable) techniques.

The ultimate goal is not keeping individual hardware running but keeping your services running. Of course hardware that fails too frequently will place a lot of stress on the rest of your cluster, so that is another reason to consider this high-end hardware... if it delivers price/performance wise. Let us take a closer look at the hardware.

The 32-Core, 64-Thread Beast
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  • haplo602 - Wednesday, August 11, 2010 - link

    This is one of the bottlenecks of your virtualised environemnt. A storage solution is only the limit if you do not use it as it was designed to be used.

    the more IO demanding application you have, the less virtualisation is going to offer any benefits. usualy CPU power is the last issue after netwrok, disk and memory.

    I had a good laugh at the opening page. High end servers are High end not because of the increased performance but because of the better management and disaster tolerance/recovery they offer. After all, they use the same CPUs and memory as the low end servers, just everything else is different (OLRAD, hot swap/plug of almost anything except memory and CPU).
    Reply
  • webdev511 - Thursday, August 12, 2010 - link

    Well, if you're willing to spend some more money on Solid State (if you go with two twelve core cpus you'll save on licences) you could stuff four of the new Fusion IO 1.28 TB Duo Drives into the box and map them as System Drives and then use attached storage for big files. Reply
  • SomeITguy - Wednesday, August 11, 2010 - link

    No offense intended, and I know this will put you on the defensive, but it sounds to me like the "development environment" was ill conceived in the design phase. You obviously overbought on processor power. The first step in designing an environment, is knowing what your apps need. You can't just buy servers, then whine about how poorly the performance matches the overall system capability...

    Last job I had Citrix Xen on HP blades with 53xx and 54xx CPU's, running about 150 production VM's. On the order of >300 total, with R&D and QA. The company had no money, and because of that we only ran local storage for the OS and most functions. The shared data we did have were on Netapps, and that alone constantly spiked up to +25k IOPS. I can't remember were each blade sat on IOPS, but it was high. I was able to balance resources utilized most of the day to about the ~60% level, with spikes hitting the high 80's. No resources being overly wasted. To do this effectively takes time and patience. You need to economize. 12 VM's on a blade with 16GB of memory was not unheard of...

    Then there is the whole ESX thing, eh, won't get into that. Again, you need to know what is going to run on the servers before you spend (waste) money.

    In my experience, It's typical that managers just override the lowly sysadmin advice, take a vendors word over the sysadmin who manages the app, or a business unit buys you the equipment without consulting, then says "here, make it work".

    Overall, I thought the article good. It is just a guide, not a bible.
    Reply
  • davegraham - Tuesday, August 10, 2010 - link

    So, i'm sitting here with a spanking new Dell R815 which is a quad socket G34 system and is shipping today w/ AMD Opteron 6176SE parts...so, this article is outdated even before it begins. (oh, did i mention it's only 2RU?)

    I'm also very curious as to what the underlying storage is for all these tests as it definitely can have an impact on the servicability of the testing.

    I'm curious as to the details per VM was well...IOMMU choices, HT sharing, NUMA settings, as well as the version of ESX being used?

    dave
    Reply
  • JohanAnandtech - Wednesday, August 11, 2010 - link

    "So, i'm sitting here with a spanking new Dell R815 which is a quad socket G34 system and is shipping today w/ AMD Opteron 6176SE parts...so, this article is outdated even before it begins. (oh, did i mention it's only 2RU?)"

    Testing servers is not like testing videocards. I can not plug the R815 in a ready installed windows pc and push the button of "Servermark". It does not work that way as you indicate yourself. A complete storage system must be set up, and in many cases ESX fails to install the first time on a brand new server. We perform a whole battery of monitoring tests for example that confirm that the DQL is low enough.

    The storage system we use for the 4 tile test is a 8 disk SSD system for the OLTP tests (described in this article). The VMs themselves sit on a separate RAID controller connect to a promise JBOD. The JBOD has 8 15000 rpm SAS disks. The only really disk intensive app is Swingbench in this test, and by making sure both data and logs get their separate SSD , we achieve DQLs under 0.1. There is lot more to the Oracle config, but if you are interested, we can share the parameter file.

    Anyway, the low DQL and the fact that we scale well from 2 tot 4 tiles shows that we are not limited by the disks.
    Reply
  • davegraham - Wednesday, August 11, 2010 - link

    johan,

    I work with VMware for a living doing platform testing for the product i support. ;) consequently, I'm very well aware of the requirements for testing VMware and the various and sundry components within the server. Hence, my slightly critical view of what you're doing here.

    appreciate the response on the storage....again, all well and good with that explanation.

    I'll put my quad socket 6176SE system against your 7500 system anyday and i'll enjoy lower rack footprint, lower power consumption, and a positively brilliant VMware experience. ;)

    keep up the good work.

    dave
    Reply
  • blue_falcon - Wednesday, August 11, 2010 - link

    If you wan to do a similar 2U config, try the R810, only has 32 dimm sockets but nearly identical to the R910. Reply
  • mapesdhs - Tuesday, August 10, 2010 - link


    Johan, how would this system compare to a low-end quad-socket Altix UV 10? (max
    RAM = 512GB).

    Ian.
    Reply
  • JohanAnandtech - Wednesday, August 11, 2010 - link

    I never tested an SGI server, so I can not say for sure. But the hardware looks (and probably is) identical to what we have tested here. Reply
  • Casper42 - Wednesday, August 11, 2010 - link

    Due to the way Dell implemented the memory on their latest Quad socket machines, if you run 2 CPUs with the FlexMem bridge, you get full memory bandwidth but half of the memory sockets are further away from the CPU due to the extra trace length of going to the empty CPU socket and through the FlexMem bridge.

    When you put in 4 CPUs you only get half the memory bandwidth of an Intel reference design. This is because the traces that would normally go to the empty CPU socket and through the FlexMem now go essentially nowhere because the CPU in that socket needs the access instead.

    I would say try IBM or HP. Just beware that IBM does some weird stuff when it comes to their Max5 memory expansion module that can also cause additional memory latency for some of the DIMM sockets and not the others.
    Reply

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