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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Mon, 26 Oct 2009 09:59:20 +0100
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Cc: hackers@freebsd.org, non@ever.sanda.gr.jp
Subject: Re: Help troubleshooting...
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On Monday 26 October 2009 01:05:03 non@ever.sanda.gr.jp wrote:
> M. Warner Losh wrote:
> > I have a usb stick (8GB) on it.  This stick has about 5GB of junk on
> > it at this point.
> >
> > I tried to do 'cat * > /dev/null' recently, to measure how fast it
> > goes.  It got about 1GB into the drive and then I got device missing
> > messages.
> >
> > So devfs thinks the device went missing:
>
> Warner-san, maybe it is caused by the hardware problem on the USB flash
> memory. Some chip on the memory might have too much heat when you access
> the memory at fast rate. Then it stops working.
>

What happens if you read from two USB disks at the same time?

If the device went missing the USB HUB signalled that. This is maybe an 
indication that the USB firmware on the device crashed. Maybe this is due to 
heat, or unhandled race conditions when the load goes high.

Try using "dd" and vary the block size from 512 to 65536 bytes. Does it stop 
working with all block sizes over time?

--HPS