linux-ext4 - Re: ext3 default journal mode

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Date:	Tue, 21 Jul 2009 13:44:07 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Ric Wheeler <rwheeler@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Stephen C. Tweedie" <sct@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Andreas Dilger <adilger@....com>,
	Chris Mason <chris.mason@...cle.com>,
	Josef Bacik <jbacik@...hat.com>, Mingming Cao <cmm@...ibm.com>
Subject: Re: ext3 default journal mode

On Mon, Jul 20, 2009 at 10:00:50PM -0400, Theodore Tso wrote:
> On Mon, Jul 20, 2009 at 07:04:03PM -0400, Valerie Aurora wrote:
> > 
> > I think it's extremely accurate and detailed, but too long - people's
> > brains turn off after about the 15th line or so.  Here's an attempt to
> > distill your description down and refer out to another document (which
> > one?) for people who want to learn more.
> 
> Fair enough;  I've created an external document here:
> 
> http://ext4.wiki.kernel.org/index.php/Ext3_Data%3DOrdered_vs_Data%3DWriteback_mode
> 
> Comments?

Nice!

> >  config EXT3_DEFAULTS_TO_ORDERED
> >  	bool "Default to 'data=ordered' in ext3"
> >  	depends on EXT3_FS
> >  	help
> > 
> >           If the mount options for an ext3 filesystem do not
> >           include a journal mode, mount it in "data=ordered" mode.
> 
> Let me give a try at this:
> 
>            The journal mode options for ext3 have different tradeoffs
>            between when data is guaranteed to be on disk and
>            performance.  The use of "data=writeback" can cause
>            unwritten data to appear in files after an system crash or
>            power failure, which can be a security issue.  However,
>            "data=ordered" mode can also result in major performance
>            problems, including seconds-long delays before an fsync()
>            call returns.  For details, see:
> 
> 	   http://ext4.wiki.kernel.org/index.php/Ext3_Data%3DOrdered_vs_Data%3DWriteback_mode
> 
>           If you have been historically happy with ext3's performance,
>           data=ordered mode will be a safe choice and you should
>           answer "y" here.  If you understand the reliability and data
>           privacy issues of data=writeback and are willing to make
>           that trade off, answer "n".

This is great.  Ship it!

-VAL
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