linux-ext4 - Re: [PATCH 1/5] jbd: strictly check for write errors on data buffers

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Message-Id: <20080604111911.c1fe09c6.akpm@linux-foundation.org>
Date:	Wed, 4 Jun 2008 11:19:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>, sct@...hat.com,
	adilger@....com, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, jbacik@...hat.com, cmm@...ibm.com,
	tytso@....edu, yumiko.sugita.yf@...achi.com,
	satoshi.oshima.fk@...achi.com
Subject: Re: [PATCH 1/5] jbd: strictly check for write errors on data
 buffers

On Wed, 4 Jun 2008 12:19:25 +0200 Jan Kara <jack@...e.cz> wrote:

> On Tue 03-06-08 15:30:50, Andrew Morton wrote:
> > On Mon, 02 Jun 2008 19:43:57 +0900
> > Hidehiro Kawai <hidehiro.kawai.ez@...achi.com> wrote:
> > 
> > > 
> > > In ordered mode, we should abort journaling when an I/O error has
> > > occurred on a file data buffer in the committing transaction.
> > 
> > Why should we do that?
>   I see two reasons:
> 1) If fs below us is returning IO errors, we don't really know how severe
> it is so it's safest to stop accepting writes. Also user notices the
> problem early this way. I agree that with the growing size of disks and
> thus probability of seeing IO error, we should probably think of something
> cleverer than this but aborting seems better than just doing nothing.
> 
> 2) If the IO error is just transient (i.e., link to NAS is disconnected for
> a while), we would silently break ordering mode guarantees (user could be
> able to see old / uninitialized data).
> 

Does any other filesystem driver turn the fs read-only on the first
write-IO-error?

It seems like a big policy change to me.  For a lot of applications
it's effectively a complete outage and people might get a bit upset if
this happens on the first blip from their NAS.

<waves vigorously at linux-ext4 people>
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