linux-kernel - Re: [Patch] document ext3 requirements (was Re: [RFD] Incrementalfsck)

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Message-ID: <20080119145317.GG24512@elf.ucw.cz>
Date:	Sat, 19 Jan 2008 15:53:17 +0100
From:	Pavel Machek <pavel@....cz>
To:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
Cc:	Theodore Tso <tytso@....EDU>, Bryan Henderson <hbryan@...ibm.com>,
	Ric Wheeler <ric@....com>, Al Boldi <a1426z@...ab.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org,
	Daniel Phillips <phillips@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Valerie Henson <val.henson@...il.com>
Subject: Re: [Patch] document ext3 requirements (was Re: [RFD]
	Incrementalfsck)

On Fri 2008-01-18 10:16:30, linux-os (Dick Johnson) wrote:
> 
> On Fri, 18 Jan 2008, Theodore Tso wrote:
> 
> > On Thu, Jan 17, 2008 at 04:31:48PM -0800, Bryan Henderson wrote:
> >> But I heard some years ago from a disk drive engineer that that is a myth
> >> just like the rotational energy thing.  I added that to the discussion,
> >> but admitted that I haven't actually seen a disk drive write a partial
> >> sector.
> >
> > Well, it would be impossible or at least very hard to see that in
> > practice, right?  My understanding is that drives do sector-level
> > checksums, so if there was a partially written sector, the checksum
> > would be bogus and the drive would return an error when you tried to
> > read from it.
> >
> >> Ted brought up the separate issue of the host sending garbage to the disk
> >> device because its own power is failing at the same time, which makes the
> >> integrity at the disk level moot (or even undesirable, as you'd rather
> >> write a bad sector than a good one with the wrong data).
> >
> > Yep, exactly.  It would be interesting to see if this happens on
> > modern hardware; all of the evidence I've had for this is years old at
> > this point.
> 
> I have a Seagate Barracuda 7200.9 80 Gbyte SATA drive that I
> use for experiments. I can permanently destroy a EXT3 file-system
> at least 50% of the time by disconnecting the data cable while
> a `dd` write to a file is in progress. Something bad happens
> making partition information invalid. I have to re-partition
> to reuse the drive.

Does turning off writeback cache on disk help? This is quite serious,
I'd say...

								Pavel


-- 
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