Sunday Oct 25, 2009

A Small and Energy-Efficient OpenSolaris Home Server

In an earlier entry, I outlined my most important requirements for an optimal OpenSolaris Home Server. It should:

  1. Run OpenSolaris in order to fully leverage ZFS,
  2. Support ECC memory, so data is protected at all times,
  3. Be power-efficient, to help the environment and control costs,
  4. Use a moderate amount of space and be quiet, for some extra WAF points.

So I went shopping and did some research on possible components. Here's what I came up with:

Choosing a Platform: AMD or Intel?

Disclosure: My wife works for AMD, so I may be slightly biased. But I think the following points are still very valid.

Intel is currently going through a significant change in architecture: The older Core 2 microarchitecture was based on the Front Side Bus (FSB), where the CPU connects to the Northbridge which contains the memory controller and connects to the memory, while also connecting to the Southbridge which connects to I/O.

Now, they are switching to the new Nehalem microarchitecture which has a memory-controller built into the CPU and a scalable I/O bus called Quickpath Interconnect that connects CPUs with other CPUs and/or IO.

Unfortunately, none of these architectures seem to support ECC memory at consumer level pricing. The cheapest Intel-based ECC-motherboard I could find had still more than double the cost of an AMD-based one. Even though the new Intel Core i7 series is based on Nehalem and thus could support ECC memory easily in theory, Intel somehow chose to not expose this feature. In addition, Core i7 CPUs are relatively new and there are not yet any power efficient versions available.

The Intel Atom processor series may be interesting for a home server from a pure power-saving perspective, but again, Atom motherboards don't support ECC and once your workload becomes a little more demanding (like transcoding or some heavier compiling), you'll miss the performance of a more powerful CPU.

AMD on the other hand has a number of attractive points for the home server builder:

  • AMD consumer CPUs use the same microarchitecture than their professional CPUs (currently, it's the K10 design). They only vary by number of cores, cache size, number of HT channels, TDP and frequency, which are all results of the manufacturing process. All other microarchitecture features are the same. When using an AMD consumer CPU, you essentially get a "smaller brother" of their high end CPUs.
  • This means you'll also get a built-in memory-controller that supports ECC.
  • This also means less chips to build a system (no Northbridge needed) and thus lower power-consumption.
  • AMD has been using the HyperTransport Interconnect for quite a while now. This is a fast, scaleable interconnect technology that has been on the market for quite a while so chipsets are widely available, proven and low-cost.

So it was no suprise that even low-cost AMD motherboards at EUR 60 or below are perfectly capable of supporting ECC memory which gives you an important server feature at economic cost.

My platform conclusion: Due to ECC support, low power consumption and good HyperTransport performance at low cost, AMD is an excellent platform for building a home server.

AMD Athlon II X2 240e: A Great Home Server CPU

An AMD Athlon II X2 240e CPU

While I was shopping around for AMD Athlon CPUs and just before I was about to decide for an AMD Athlon II X2 variant, AMD offered me one of their brand new AMD Athlon II X2 240e for testing, provided that I blogged about it. Thank you, AMD!

Introduced in October 20th, this CPU is part of the newest energy-efficient range of consumer CPUs from AMD. It has 2 cores (hence X2), snazzy 2.8 GHz and a 2 MB L2 cache. What's most important: The TDP for this CPU is only 45W, meaning that even under the highest stress, this CPU will never exceed 45W of power consumption. Including the memory controller. As you've guessed already, the "e" in the model number stands for "efficient".

There's an important trade-off to consider for home server CPUs: For instance, the AMD Phenom II series would have been more powerful because it has an additional L3 cache, but their TDP is at 65W minimum. While big caches (both with AMD and Intel) are good for compute-intensive operations and games, they can't help much in a home server context: Home servers spend most of their non-idle time transferring data from A to B (files, videos, music) and a cache doesn't help much here, cause it's just another stop between I/O and CPU to pass by. Transferred data hardly gets re-used.

Instead, for home servers, sacrificing the L3 cache for lower power consumption makes a lot of sense: You pay less for the CPU and you pay less for your power bill without sacrificing too much (if any) server relevant performance.

My CPU conclusion: For home servers, AMD Athlon II "e" series are perfect, because they save power and money and do the job very well. For games you might choose a more powerful Phenom II processor, which delivers better compute power at a slightly higher power bill.

Finding the Right Motherboard

After nailing the Platform and CPU question, I needed a motherboard. This can be a confusing process: For each CPU there are different chipsets, then there are different vendors offering motherboards based on these chipset, and then they offer different variants with different features. What should a good home server motherboard offer?

  • OpenSolaris support: Most motherboards "just work" with OpenSolaris, especially if they've been available for some time and/or use some well-known chipsets. To remove any doubts, consult the OpenSolaris Hardware Compatibility List.
  • ECC: Yes, AMD's ECC support is in the CPU, but just in case, we want to make sure that the motherboard exposes this feature to the user.
  • Integrated graphics: We only need a graphics card for installation, BIOS-settings/updates or debugging. The graphics shouldn't consume much power and doesn't need to deliver a lot of performance. Therefore, integrated graphics is just fine for a home server, and it saves some precious slot space, too.
  • Enough SATA ports: You need two ports for a mirrored root pool, another two for a mirrored data pool and then some more for hot-spare or if you want to spread your data pool across 4 or more disks. Many motherboards come with 6 SATA ports, which is ok.
  • Stability: If you have the choice between different variants, try to go for the "business" or "quality" version. It will likely have slightly better components and be better tuned towards 24/7 operation than the "performance", "gaming" or "overclocker" type boards which try to squeeze out more performance at the expense of durability.

Here's a very useful email thread on the OpenSolaris ZFS-discuss mailing list about CPU and motherboard options, pros and cons and user experiences. In this discussion, F.Wessels recommended the M3A78 series from Asus so I went for the M3A78-CM motherboard, which is their "business class" variant, priced at around 60 Euros and it has 6 SATA and 12(!) USB ports.

My motherboard conclusion: The Asus M3A78-CM motherboard has everything I need for a home server at a very low cost, and it's proven to run OpenSolaris just fine.

The Case: Antec NSK-1380

I won't go into much details about the case. My goal was to find one that can support at least 4 disks while being as compact as possible. The Antec NSK-1380 was the smallest case I could find that supports 4 disks. It comes with a built-in power supply, an extra fan, some features to help with keeping noise down and it looked ok for a PC case.

Miscellaneous Tips&Tricks

While putting everything together, I ran into some smaller issues here and there. Here's what I came up with to solve them:

  • CPU cooler: My CPU being a gift from AMD, it came without a cooler. I chose the Zalman CNPS 7000C AL-CU because it was the cheapest cooler that was less than 6cm high, which is a limit imposed by the case. Unfortunately, it collides with one of the 4 harddisk slots by a mere couple of millimeters, so I need to figure out how to best cut or bend the blades to make room for the disk without hurting the cooler too much. I'm not very familiar with PC CPU coolers, but I suspect that with 45W TDP one could even get away with a passive cooler. The Zalman came with a throttle circuit which I set to the minimum speed. This seems to be more than enough and it makes the system really silent, but I need some more thorough testing to confirm. Drop me a comment if you are familiar with passive cooling of 45W TDP CPUs.
  • Boot disks: We need something to boot our home server from, so boot disks are unavoidable. I say "disks", because they should always be mirrored. But other than providing a way of booting, they tend to get in the way, especially when space is a precious resource in a small case. Some people therefore boot from CF cards or other small flash media. This can be a nice solution, especially combined with an IDE-to-CF adapter, but consumer level flash media is either very slow (a typical OS install can take many hours!) or very expensive. While looking for alternatives, I found a nice solution: The Scythe Slot Rafter fits into an unused PCI slot (taking up the breadth of two) and provides space for mounting four 2.5" disks at just EUR 5. These disks are cheap, good enough and I had an unused one lying around anyway, so that was a perfect solution for me.
  • Extra NIC: The Asus M3A78-CM comes with a Realtek NIC and some people complained about driver issues with OpenSolaris. So I followed the advice on the aforementioned Email thread and bought an Intel NIC which is well supported, just in case.
  • USB boot: I couldn't get the M3A78-CM to boot from USB at all. I tried a USB stick and a USB disk and different boot settings in the BIOS to no avail. I gave up and built in a DVD-ROM drive from my old server just to install OpenSolaris, then built it out again. Jan Brosowski has the same motherboard and he found out that you need to update to the latest BIOS revision and use the USB port that's right below the Ethernet port for USB boot to work. YMMV :).

The Result

And now for the most important part: How much power does the system consume? I did some testing with one boot disk and 4GB of ECC RAM and measured about 45W idle. While stressing CPU cores, RAM and the disk with multiple instances of sysbench, I could not get the system to consume more than 80W. All in all, I'm very pleased with the numbers, which are about half of what my old system used to consume. I didn't do any detailed performance tests yet, but I can say that the system feels very responsive and compile runs just rush along the screen. CPU temperature won't go beyond the low 50Cs on a hot day, despite using the lowest fan speed, so cooling seems to work well, too.

I just started full 24/7 operation of my new home server this weekend, so I hope I'll have some more long-term experience about performance and stability in a few months. Meanwhile, I'm in the middle of configuring the system, installing some services and implementing a new way of managing my home server. But that's probably the topic of another blog post...

Do you agree with the home server conclusions I reached in this post? Or would you suggest alternatives? Do you have experiences to share with the mentioned components? Or do you have suggestions and tips on how to get the most out of them? Let me know by posting a comment here!

Many thanks go to Michael Schmid of AMD for sending me the AMD Athlon II X2 240e CPU.

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