Software Raid 5 on Atom

I plan to build a frugal Raid 5 file server that will also download torrents and act as a Mthtv backend (requires Mysql) for a hardware assisted tv card such as Hauppauge 1600. I only use the analog side of the tv card so the CPU draw is pretty trivial. Likely, I will run the current version of Ubuntu server and utilize its software raid feature. I am trying to assess how software raid will impact CPU utilization. Specifically, I am trying to figure out whether a single core Atom variant will be adequate. Currently I am testing an Atom 330 in an Ubuntu 9.04 desktop box lacking raid and it kinda looks like a single core is more than adequate for all target activities except software raid 5 which is not available for testing. The box will use wi-fi but this should not impact CPU utilization.

The new box will be a home media server and the worst case file server requirements basically would require simultaneous save of a tv recording (2.2 Gb/hr) while playing a media file (2.2 Gb/hr) some torrent activity (under 120 Kb/sec combined read and write) and maybe open an office application. My impression is that the CPU draw relates to total file operations (calculating parity). This scenario looks like it is under 1.5 Mb/hr. Any insight or relevant perspective would be appreciated.

Also, any insight on whether Intel's Matrix Storage technology would be helpful in this scenario would be appreciated. My initial reaction is that it may be most helpful in failure recovery but should not otherwise impact performance. Sounds like it is worth $25 to me.

Likely, after Pineview is released (with 4 sata connectors) I will visit either Singapore or Honk Kong to purchase components in a jurisdiction with a more favorable excise tax regime.
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  1. You're running Ubuntu now, what kind of disks do you have? You can test the disk throughput and also probably also the performance on raid5, assuming you can free up the disks for testing. 2.2GiB per hour means only 625KiB/s which should not be a problem. But you should know raid5 isn't slow because it has to calculate parity, it requires high cpu utilization because of many memory operations. The parity calculation itself goes at the speed of memory in my testing. If you want to test the throughput of your disks, you can use the command below. But do not make mistakes with the dd commands, especially the of= is important, since this is the device that will be written to:

    sudo dd if=/dev/sdX of=/dev/null bs=1M count=1000

    Replace the X in /dev/sdX to the disk name, for example /dev/sde.

    Unfortunately, the Atom is not a very powerful CPU. And while its very power efficient, its often combined with an old intel chipset that uses 10 times more power than the CPU. Obviously this isn't a favorable platform. VIA CN is faster and has PCI-express. The Intel-chipsets do not support this, and was done to prevent the Atom from cutting profits in the laptop sector. Intel doesn't want the Atom to support HD-movies, for example. This is a marketing/strategic decision and not a technical one. The Atom can support HD just fine with nVidia ION chipset. Also know that the total system power consumption of an Atom board is not less than a AMD dualcore IGP system, which is much more powerful and only slightly more expensive.

    And as you may know, the Intel Matrix RAID drivers are Windows-only drivers so they are not available on Linux. Linux uses its own implementation: md-raid. No hardware acceleration is performed on the RAID with chipsets supporting RAID. So you can't use the intel-drivers on Linux.
  2. Currently, I have a single WD10EACD drive which has 1 Tb capacity. I will migrate to raid 5 for protection against single disk failure and also for capacity expansion. I neither have nor plan to acquire any kind of backup capability. I observe no current issue with throughput and do not anticipate any plan to implement any sort of HD capability during the next 4 years or more. Locally, they have not yet specified the country's HD broadcast standard so there may be some lag before this becomes an issue. I have zero interest in games and any transcoding will be done on a different frontend box.

    I agree that Atom with my 945GC chipset is a cheap, energy inefficient, wimpy processor. The SCH chipsets such as US15W fix the energy efficiency issue but, so far, lack 4 sata ports. Pineview will fix the energy efficiency issue pretty convincingly and I hope it will offer 4 sata connectors.

    If I interpret your response correctly, I think you are speculating that the only thing wimpier than atom are the requirements of my intended use: it may be sub-optimal but I have lowered the bar enough that it may work

    Ion is a fascinating and worthy chip set but I do not think it is targeted towards a server that will not have a monitor attached. I will review Via's CN chip set but currently it is not offered on any itx motherboard from Pricewatch so it is hard to evaluate its economy. Locally, energy cost about US $0.25 per Kw/hr. A 10 watt draw in a 24 X 7 server cost about $22/year or $66 over a 3 year life. That number largely drives the decision of what makes a motherboard economical

    You are spot on that Intel Matrix technology does not work with raid 5 in Linux (though 0 and 1 are maybe ok). I appreciate the heads up.
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