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So I'm trying to install more than 127 usb devices into one computer for a project for school. Every year my school hands out a bunch usb drives to each ...
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  1. #1
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    >33 USB drives, is it possible?


    So I'm trying to install more than 127 usb devices into one computer for a project for school.

    Every year my school hands out a bunch usb drives to each graduate. I managed to get permission to borrow them before they hand them out.

    I want to raid them all together.
    -- For science.

    Why 127?
    --It's the maximum theoretical limit, per host controller

    Hubs count towards the 127 device limit.

    The problem I'm having is I can't get an operating system to recognize more than 36 of them at once.

    Here are my results so far.

    Windows 7 turns off the usb port at 36 usb drives and I have to unplug all the usbs and restart to get it working again.

    Linux (Ubuntu 10.04) stops recognizing more usb drives after 33. I have no clue why it is failing so far short of 127.

    The box has 4 externally powered 10 port hubs, each with 10 usb drives plugged into them which is then plugged into the motherboard. From a power consumption standpoint this should be providing 1.5Amps to each hub and each drive shouldn't be pulling more than 100mA when constantly writing. So I should be good.

    ChromeOS (linux I know) stops recognizing drives after 16, haven't played with dev mode.

    OSX does funky stuff when 20 get plugged in, it somehow recongizes 23.

    Has anyone else dived down this path before?

    Proof I'm not just messing with you guys is attached.
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  2. #2
    Trusted Penguin Irithori's Avatar
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    Hi and welcome

    you are right, it should be possible.
    Be aware, that the host controller also counts as a usb device, but this still makes 126.

    Why only 32..
    - As all operating systems have trouble: Maybe the usb host controller chip (unlikely) or the usb hub introduce a arbitrary, non-standard limit.
    - things tend to get weird, if you go out of the "norm"

    I would start simple.
    Plug in just one of the hubs and list the hierarchy:
    Code:
    lsusb -t
    Then add 10 usb drives, list the hierarchy again
    Plug in the next hub, list the hierarchy
    rinse, repeat

    All the time watch dmesg for errors.
    You must always face the curtain with a bow.

  3. #3
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    Awesome thanks for the response. Glad to know I'm not alone.

    Alright so it might be a power issue.

    I've been playing with Windows and started out with 5 usb drives to each hub and then slowly started adding one more to each hub which surprisingly worked.
    I got to 99 usb drives, using 12 hubs, 3 host controllers, and one usb for keyboard and mouse(logitech combo). Then the whole machine BSOD'd some usb controller error.

    I'll rinse and repeat again tomorrow with linux.

    There are 7 root usb controllers listed in device manager for windows, I'm not sure if they count towards the limit even if nothing is plugged into them.

  4. #4
    Trusted Penguin Irithori's Avatar
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    Hubs do count as devices.
    You must always face the curtain with a bow.

  5. #5
    Linux User Steven_G's Avatar
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    Could it be a wattage issue? You're stating your power consumption in Volt-amps. However, with small computer equipment like dektops and laptops the PSUs are usually capacitor input supplies that have Watt ratings in the range of .55 to .75 times the VA rating (power factor of 0.55 to 0.75).

    So even if you're in range on the apparent power you could very easily be drawing more Wattage than the PSU(s) can handle.

  6. #6
    Linux Guru Rubberman's Avatar
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    Most workstation and server class systems have 2 or 3 USB controllers. Hubs count as 1 device, and there may be other cruft that counts as well. So, assuming you have 3 controllers on your mobo, you MIGHT be able to get 32x3 devices connected and running, although you will definitely want them, or the hubs they are connected to, to be externally powered. There is NO WAY, your USB controllers can power that many devices, even if they are low-power like thumb drives, etc.

    Why 32 devices or so? Well, it may be that although the USB spec says that up to 127 devices can be attached, it is NOT required for the controller manufacturers to support that many. Consider it an "up to" number. Ditto OS support.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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