linux-kernel - Re: usb hdd problems with 2.6.27.2

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Message-ID: <4905D986.6050001@panasas.com>
Date:	Mon, 27 Oct 2008 17:08:54 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	dgilbert@...erlog.com
CC:	Alan Stern <stern@...land.harvard.edu>,
	Luciano Rocha <luciano@...otux.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	SCSI development list <linux-scsi@...r.kernel.org>
Subject: Re: usb hdd problems with 2.6.27.2

Douglas Gilbert wrote:
> 
> Since the READ CAPACITY "off by one" error is so common,
> perhaps drivers such as usb-storage could have a hook to
> do a pseudo READ CAPACITY. Then if the capacity value
> looked odd (in both senses) the driver could do an IO to
> the suspect block and if that failed decrement the capacity
> value passed back to the mid level.
> Put another way, why don't these defective devices trip up
> another OS?
> 

Window$ never reads the last sector unless it is actually written
to. I had such a device it got stuck when I wrote to the
last sector.

> BTW a single disk in RAID 0 (seen on a HP E200 controller)
> has a shortened capacity value seen in the midlevel on the
> corresponding logical drive. That missing chunk is probably
> where the RAID controller puts its control information.
> Anyway, playing with the capacity value returned by READ
> CAPACITY certainly has a precedent.
> 
>> Later on the system tries to read the contents of what it thinks is the 
>> last sector:
> 
> I know that happens but it seems strange that upper levels
> are reading a block that has never been written to. Read ahead?
> 

That would be udev or hald, I can't remember which. It is a special Linux
fixture. ;)

> Doug Gilbert
> 
> 

Boaz
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