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Old 02-14-2013, 01:40 AM   #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.

Quick update. I got to 99 drives using 12 hubs. Seems to be a power issue. Windows reports each drive is using 200mA. If you start with 5 drives and add one at at time it will go past the 33 drive limit I was dealing with. Windows BSOD'd on me so I'm gonna try with linux and order more hubs so I can spread it out more.
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Last edited by jimbob3000; 02-14-2013 at 03:12 AM.
Old 02-14-2013, 09:48 AM   #2
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Look at: Programming Guide for Linux USB Device Drivers

How are you chaining the USB hubs to the system? Cable lengths between hubs? As to the power requirements, you should consider isolating each external hubs that you now have and providing more external power to each.

I am curious as to why and what you are going to use that many external USB devices.

As for Linux, you will need to look at the kernel USB driver and configuration.
Old 02-14-2013, 04:52 PM   #3
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I'd be ordering more pci-e to usb adapter cards.


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