linux-kernel - Re: document ext3 requirements

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Date:	Tue, 27 Jan 2009 14:24:27 +0100
From:	Thierry Vignaud <tvignaud@...driva.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Rob Landley <rob@...dley.net>, Theodore Tso <tytso@....edu>,
	Pavel Machek <pavel@...e.cz>,
	Sitsofe Wheeler <sitsofe@...oo.com>,
	Duane Griffin <duaneg@...da.com>, Valdis.Kletnieks@...edu,
	Martin MOKREJŠ <mmokrejs@...osome.natur.cuni.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com,
	rdunlap@...otime.net, linux-doc@...r.kernel.org
Subject: Re: document ext3 requirements

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

> > That would be true if the disk hardware wasn't doing a gazillion retries to 
> > read a bad sector internally (taking 5 seconds to come back and report 
> > failure), and then the darn scsi layer added another gazillion retries on top 
> > of that, and the two multiply together to make it so slow that that when you 
> > leave the thing copying the disk overnight it's STILL not done 24 hours later.  
> > Going in and cherry picking individual files looks kind of appealing in that 
> > situation.
> 
> You could of course just learn to use the functions the kernel provides.
> If you want to recover disk blocks without retrying you can do that via
> SG_IO. If you want to adjust the timeout and retry levels you can do that
> too via sysfs.

Sure but maybe the default values might be altered. I think the current
tradeoff has set the cursor way too far for retries.

I remember seeing I/O error on CDs resulting in zillions of retries on
errors on USB discs resulting in resetting the USB port again & again
for hours... (CD case is years ago, but I usually see the USB layer
trying reseting for quite a long time at least once per month)
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