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List:       linux-usb-devel
Subject:    [linux-usb-devel] Re: [Linux-usb-users] USB slows down after a few minutes
From:       Alan Stern <stern () rowland ! harvard ! edu>
Date:       2006-01-28 15:31:18
Message-ID: Pine.LNX.4.44L0.0601281023420.19283-100000 () netrider ! rowland ! org
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On Fri, 27 Jan 2006, Igor Yakushin wrote:

> Here is another test attached. However, this test has been running for three hours without
> crashing. So I have BEFORE and DURING parts but not AFTER. First I plugged 2 external drives and
> one memory stick and executed
> 
> usb.py /media/usbdisk3/out
> 
> Two hour later I plugged another memory stick. And it is still running without crashing although
> it is now very slow (according to iostat -kx -d 5 the write speed the the external USB disk is
> about 1000 kB/s). However, it is not obvious to me whether it is slow because of the way the
> script is written or because USB slowed down. I do not think USB itself slowed down because I can
> browse the disks interactively and open files there without noticing any performance problems. So
> I guess it is the program that is now writing to a file too slow (perhaps because the file is
> already 21 GB).

There's no way of telling how slow the transfer is from the logs, because 
the logs don't include any timestamps.

> That's the first time USB survived for so long. I wonder what's different.
> Might it have something to do with the number of plugged USB devices?
> Yesterday the same test crashed USB within minutes.

Probably nothing is different and you're seeing random hardware faults.

> Is there some standard test set to diagnose USB problems?

No, no software test.  Many problems can be diagnosed only with a hardware 
bus analyzer.

> Also, I wonder what's the best forum/person to discuss the sata drive problems (not sure if they
> are of the same origin as USB problems or different and not sure how to reproduce or describe them
> yet).

In case of doubt, post on LKML.

Alan Stern



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